CBSE CLASS X SCIENCE General Instructions:

Transcription

1 CBSE CLASS X SCIENCE General Instructions: (i) (ii) (iii) (iv) (v) (vi) (vii) (viii) The question paper comprises of two Sections, A and B. You are to attempt both the sections. All questions are compulsory. There is no overall choice. However, internal choice has been provided in all the three questions of five marks category. Only one option in such questions is to be attempted All questions of Section A and all questions of Section B are to be attempted separately Questions number 1 to 4 in Section A are short answer type questions. These questions carry one mark each Questions number 5 to 13 in Section A are short answer type questions. These questions carry two marks each Questions number 14 to 22 in Section A are also short answer type questions and carry three marks each Questions number 23 to 25 in Section A are long answer type questions and these questions carry five marks each Q1 (i) CH 3 COCH 3 Functional Group: Ketone O (ii) Formula C C 2 H 5 CHOOH Functional Group: Carboxylic acid OH Q2 Scattering is the phenomena responsible for making the path of light visible. When a beam of light interacts with particles of a medium it is redirected in many different direction.

2 Q3 The synthetic chemical, chlorofluorocarbons (CFCs) containing halogen as functional group is responsible for the depletion of ozone layer. Q4 Non-biodegradable substance are: Milk bags and tin cans. Q5 Puberty is the process of physical changes by which a child s body matures into an adult body capable of sexual reproduction to enable fertilization. Two changes observed in girls at this stage are: (i) (ii) Increase in breast size Start of menstruation Q6 Asexual reproduction is a mode of reproduction in which offspring arises from a single parent. Binary fission and budding are two forms of asexual reproduction. Q7 Advantages of water stored in the ground are: (i) (ii) (iii) (iv) It does not evaporate and is available to wells. It does not provide breeding grounds for mosquitoes etc. It provides moisture for vegetation over a wide range. It is also protected from contamination by human and animal waste. Q8 Fossil fuels are composed of carbon, hydrogen, nitrogen and sulphur. When these are burnt, the products are CO 2, H 2 O, oxides of nitrogen and sulphur. Incomplete combustion of fossil fuels produces green house gases such as CO 2. If huge amount of fossil fuels are burnt, it would produce high amount of CO 2 resulting intense global warming. Q9 The first prism disperses white light into its seven constituent colors and forms the spectrum. The other inverted prism recombines all the seven colors and gives a white light.

3 Q10 Properties of the image by a concave mirror when object is placed between focus and pole of the mirror, (i) (ii) (iii) (iv) Virtual Erect Magnified Image is formed behind the mirror Q11 Atomic number of M = 12 Q12 (i) Electronic configuration : 2, 8, 2 (ii) Since, the valence shell contains 2 electrons, it belongs to group 2. (iii) M is a metal. (iv) The formula of its chloride is M Cl 2. If electronic configuration is known, then the valency of an element is determined by the number of valence electrons present in the outermost shell. The electronic configuration of an element of atomic number 9 is 2, 7. It requires one electron to get stable noble gas configuration. Hence its valency is 1. Q13 A star sometimes appears brighter and some other times fainter, this effect is called as twinkling effect. This effect arises due to atmospheric refraction. Our atmosphere is constantly moving. Light travelling from the stars gets bent in different directions making them twinkle. Q14

4 (i) F, Cl, Br belong to same group 17. Atomic size increase down the group. This is because new shells are added. Br has 4 shells, as compared to 2 and 3 in F and Cl respectively. Hence, Br has the largest atomic radius. (ii) F is most reactive due to smaller size, high effective nuclear charge and high electro negativity. Q15 STD stands for Sexually Transmitted Disease. These diseases transmitted during sexual intercourse. STDS caused due to (i) Bacterial infection Gonorrhea Syphilis (ii) Viral infection AIDS Herpes The spread of these diseases can be prevented by advocating the use of condoms.

5 Q16 Q17 The wings of a bird and a bat are similar in function but this similarity does not mean that these animals are more closely related. If we carefully look at these structures, then we will find that the wings of a bat are just the folds of skin that are stretched between its fingers whereas the wings of birds are present all along the arm. Therefore, these organs are analogous organs. Evolution is the cumulative changes that occur in a population over time. It is the result of change in the genetic makeup of the organism due to mutations and other sources of variation. The favorable mutations are accepted by nature and provide the organism an adaptive advantage. Evolution ultimately results into speciation. Evolution cannot always be equated to progress because

6 Evolution does not always lead to the formation of a new species. The newly formed species as a result of evolution may have complex organization but cannot be considered better to the earlier species. Evolution simply leads to diversification. Q18 Blue colour flower plant BB White colour flower plant bb The cross involved is as follows: Blue Colour Flower White Colour Flower BB bb Q19 (a) In F 1 generation, all plants will have blue flower. (b) In the F 2 generation, 25% of flowers are white in color. (c) The ratio of the genotypes BB and Bb in the F 2 generation would be 1(BB) : 2 (Bb). (a) CH 4 + O 2 CO 2 + H 2 O + Heat and Light

7 (b) CH 2 + H 5 OH (c) CH 3 COOH + NaOH Hot Conc. H2SO4 CH 2 = CH 2 + H 2 O CH 3 COONa + H 2 O Q20 The defect of vision is myopia. It can be corrected by using a concave lens of suitable power. Following are the ray diagrams: (i) Defect of vision. (ii) For its correction. Q21 Convex mirrors give a virtual, erect, and diminished image of the objects placed in front of them. They are preferred as a rear-view mirror in vehicles because they give a wider field of view, which allows the driver to see most of the traffic behind him.

8 Concave mirrors are used for shaving as it gives larger and erect image of the face. Q22 Q23

9 Sign conventions for spherical mirrors I. Objects are always placed to the left of the mirror i.e. light must fall on the mirror from left to right. II. All distances are measured from the pole of the mirror. III. Distances along the direction of the incident ray (along positive X-axis) are taken as positive. IV. Heights measured perpendicular to and above the principal axis (along positive Y-axis) are taken as positive. V. Heights measured perpendicular to and below the principal axis (along negative Y-axis) are taken as negative. Given, m = -3 (real image is inverted always) u = 16 cccc

10 Now, m = vv uu = -3 = v 16 v = 48 cccc vv = v ( 16) 16 Using mirror formula, 1 f 1 f = 1 v + 1 u = = 1 ( 48) ( 16) 12 f = 12 cccc OR The law of refraction that defines the refractive index of a medium with respect to the other is given by first law of refraction known as Snell s law. First law of refraction The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant. This is known as Snell s law. Mathematically, it can be given as follows: sin i sin r = constant = a µ b Here, a µ b is the relative refractive index of medium b with respect to medium a. consider a ray of light travelling from medium B into medium A. let v 1 be the speed of light in medium A and v 2 be the speed of light in medium B. then the refractive index of medium A with respect to medium B is given by n AB = v 2 v 1 If one medium is vacuum or air then the constant is named as absolute refractive index of the medium. Let, absolute refractive index of glass, n g = 3 2 Absolute refractive index of water, n w = 4 3 Speed of light in glass, v g = m/s (i) Speed of light in vacuum

11 (ii) Speed of light in water, Q24 Soaps are potassium or sodium salts of long chain carboxylic acid. On the other hand, detergents are ammonium or sulphonate salts of long chain carboxylic acid. Action of soap in removing an oily spot from a shirt The dirt present on clothes is organic in nature and insoluble in water. Therefore, it cannot be removed by only washing with water. When soap is dissolved in water, its hydrophobic ends attach themselves to the dirt and remove it from the cloth. Then, the molecules of soap arrange themselves in micelle formation and trap the dirt at the centre of the cluster. These micelles remain suspended in the water. Hence, the dust particles are easily rinsed away by water. Soap does not work properly when the water is hard.

12 A soap is a sodium or potassium salt of long chain fatty acids. Hard water contains salts of calcium and magnesium. When soap is added to hard water, calcium and magnesium ions present in water displace sodium or potassium ions from the soap molecules forming an insoluble substance called scum. A lot of soap is wasted in the process. OR Difference in physical properties of ethanol and ethanoic acid Ethanol It is liquid at room temperature. Ethanoic acid It often freezes in winter. Its melting point is 156 K. Its melting point is 290 K. Its melting point is 351 K. Its boiling point is 391 K. Difference in chemical properties of ethanol and ethanoic acid Ethanol Ethanoic acid 1. It releases hydrogen gas on reaction 1. It does not release hydrogen gas on with metallic sodium. reaction with metallic sodium. 2. It does not release carbon dioxide 2. It releases carbon dioxide gas on reaction gas on reaction with sodium bicarbonate. with sodium bicarbonate. Q25 Pollination is the process in which the transfer of pollen grains takes place from anther to stigma for the purpose of fertilization in plants. Fertilization refers to the fusion of male and female gamete. Diagram of pistil showing formation of pollen tube

13 OR 1. Testis: The testes are the male reproductive organs that are located outside the abdominal cavity within a pouch called scrotum. It produces sperms and also produce a hormone called testosterone, which brings about secondary sexual characters in boys. 2. Seminal vesicles: Seminal vesicles secrete mucus and alkaline fluid that helps the sperm to swim and also neutralizes the acidic condition in vagina. 3. Vas deferens: It carries sperm from the vasa efferentia to the urethra. 4. Ureter: When blood is filtered by the kidney, the waste material (urine) is passed on to urinary bladder via the ureters. The function of ureter is to carry urine from the kidney to the urinary bladder. 5. Prostate glands: It produces an alkaline fluid (prostatic fluid), which is a constituent of the semen. The prostatic fluid provides motility, longer survival period (neutralizes the acidic environment of the female reproductive tract) and protection to sperms. Q26 Both amoeba and yeast are unicellular organisms. In Amoeba, a single cell divides to give rise to two identical daughter cells by the process of binary fission. In yeast, the cells reproduce by the process of budding. The Correct Answer is A Q27 During budding in yeast, a single cell develops a protrusion wherein the nucleus divides to give rise to two daughter nuclei. One of the daughter nucleus migrates into the protrusion to form a bud. This bud then enlarges in size and may undergo budding while attached to the parent cell. Hence, budding results in a chain of cells.

14 The Correct Answer is D Q28 The correct order of steps is a, d, c, b. The Correct Answer is C Q29 During binary fission, a single cell gets divided into two equal and identical daughter cells. The Correct Answer is C Q30 The raisins after being soaked in water are dried on a piece of filter paper in order to remove the excess water present on their surface. The Correct Answer is D Q31 The percentage of water absorbed by raisins is calculated by using the formula W 2 W 1 W 1 x 100 where, W 2 is the weight of wet raisin and W 1 is the weight of dry raisin. The Correct Answer is D Q32 The odour of vinegar is same as that of acetic acid. Also, being an acid (through weak) it turns blue litmus to red. The Correct Answer is D Q33 Acetic acid reacts with Na 2 CO 3 to form sodium acetate, carbon dioxide and water. It is the colourless gas carbon dioxide gas which comes out as bubbles. The Correct Answer is C

15 Q34 Acetic acid forms a homogeneous solution with water. The Correct Answer is D Q35 Cu is present in +2 oxidation state and iron is present in +3 oxidation state. The Correct Answer is D Q36 Reaction in beaker X: Fe + CuSO 4 (blue) Reaction in beaker Y: Zn + FeSO 4 (green) FeSO 4 (green) + Cu ZnSO 4 (colourless) + Fe The Correct Answer is D Q37 Using Snell s law, sin i/sin r = n 2 /n 1, check the ratio of the sine values of I and r which gives 1.5 (we know, n 2 = 1.5 and n 1 = 1) will be the answer. The Correct Answer is D Q38 Incident and emergent angles are measured from the normal of the plane. The Correct Answer is C Q39 The correct sequence of steps is c, d, a, e, b. The Correct Answer is B Q40 Screen is moved to get the focused image for a fixed object and mirror position. The Correct Answer is A Q41

16 Focal length is the distance between the focus and the mirror. The image of the distant object forms at the focus of the mirror. The Correct Answer is B

17 CBSE CLASS -X -SCIENCE General Instructions: (i) (ii) (iii) (iv) (v) (vi) (vii) (viii) The question paper comprises of two Sections, A and B. You are to attempt both the sections. All questions are compulsory. All questions of Section-A and all questions of Section-B are to be attempted separately. Question numbers 1 to 3 in Section-A are one mark questions. These are to be answered in one word or in one sentence. Question numbers 4 to 7 in Section-A are two mark questions. These are to be answered in about 30 words each. Question number 8 to 19 in Section-A are three marks questions. These are to be answered in about 50 words each. Question numbers 20 to 24 in Section-A are five marks questions. These are to be answered in about 70 words each. Question numbers 25 to 42 in Section-B are multiple choice questions based on practical skills. Each question is a one mark question. You are to select one most appropriate response out of the four provided to you. Section A Q1 How many vertical columns are there in the modern periodic table and what are they called?(1) Q2 What is speciation? (1) Q3 Why biodegradable and non-biodegradable wastes should be discarded in two separate dust bins? (1) Q4 The chromosomes number of the sexually reproducing parents and their offspring is the same. Justify this statement. (2) Q5 A ray of light incident on a rectangular glass slab immersed in any medium emerges parallel to itself. Draw labeled ray diagram to justify this statement. (2) Q6 We often observe domestic waste decomposing in the bylanes of residential colonies. Suggest ways to make people realize that the improper disposal of waste is harmful to the environment. (2) Q7 List and explain any two advantages associated with water harvesting at community level. (2)

18 Q8 Write the name and the structural formula of the compound formed when ethanol is heated at 443 K with excess of conc. H 2 SO 4. State the role of conc. H 2 SO 4 in this reaction. Write chemical equation for the reaction. (3) Q9 Why homologous series of carbon compounds are so called? Write chemical formula of two consecutive members of a homologous series and state the part of these compounds that determines their (i) physical properties, and (ii) chemical properties. (3) Q10 Given below are some elements of the modern periodic table: (3) 4Be, 9 Fe, 14 Si, 19 K, 20 Ca (i) (ii) (iii) Select the element that has one electron in the outermost shell and write its electronic configuration. Select two elements that belong to the same group. Give reason for you answer. Select two elements that belong to the same period. Which one of the two has bigger atomic size? Q11 Write the number of periods the modern periodic table has. How do the valency and metallic character of elements vary on moving from left to right in a period? How do the valency and atomic size of elements vary down a group? (3) Q12 (a) Explain the process of regeneration in Planaria. (3) (b) How is regeneration different from reproduction? Q13 Write two examples each of sexually transmitted diseases caused by (i) virus, (ii) bacteria. Explain how the transmission of such diseases be prevented? (3) Q14 Tabulate two distinguishing features between acquired traits and inherited traits with one example of each. (3) Q15 The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it. Justify this statement with the help of flow chart showing determination of sex of a newborn. (3) Q16 Mention the types of mirrors used as (i) rear view mirrors, (ii) shaving mirrors. List two reasons to justify your answers in each case. (3) Q17 An object of height 6 cm is placed perpendicular to the principal axis of a concave lens of focal length 5 cm. use lens formula to determine the position, size and nature of the image if the distance of the object from the lens is 10 cm. (3)

19 Q18 State the difference in colors of the sun observed during sunrise/sunset and noon. Give explanation for each. (3) Q19 (a) What is an ecosystem? List its two main components. (3) (b) We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly. Explain Q20 (a) Define the term isomers. (5) (b) Draw two possible isomers of the compound with molecular formula C 3 H 6 O and write their names. (c) Give the electron dot structure of the above two compounds. Q21 (a) List three distinguishing features between sexual and asexual types of reproduction. (5) (b) Explain why variations are observed in the offspring s of sexually reproducing organisms? Q22 (a) Identify A, B and C in the given diagram and write their functions. (5) (b) Mention the role of gamete and zygote in sexually reproducing organisms. Q23 (a) State the laws of refraction of light. Give an expression to relate the absolute refractive index of a medium with speed of light in vacuum. (5) (b) The refractive indices of water and glass with respect to air are 4/3 and 3/2 respectively. If the speed of light in glass is 2 x 10 8 ms -1, find the speed of light in (i) air, (ii) water. Q24 (a) A person cannot read newspaper placed nearer than 50 cm from his eyes. Name the defect of vision he is suffering from. Draw a ray diagram to illustrate this defect. List its two possible

20 causes. Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length. (5) (b) We see advertisements for eye donation on television or in newspapers. Write the importance of such advertisements. Section B Q25 A student takes 2 ml acetic acid in a dry test tube and adds a pinch of sodium hydrogen carbonate to it. He makes the following observations: (1) I. A colorless and odourless gas evolves with a brisk effervescence. II. The gas turns lime water milky when passed through it. III. The gas burns with an explosion when a burning splinter is brought near it. IV. The gas extinguishes the burning splinter that is brought near it. The correct observations are: (A) I, II and III (B) II, III and IV (C) III, IV and I (D) IV, I and II Q26 In an experiment to study the properties of acetic acid a student takes about 2 ml of acetic acid in a dry test tube. He adds about 2 ml of water to it and shakes the test tube well. He is likely to observe that: (1) (A) The acetic acid dissolves readily in water (B) The solution becomes light orange (C) Water floats over the surface of acetic acid (D) Acetic acid floats over the surface of water Q27 A student prepared 20% sodium hydroxide solution in a beaker containing water. The observations noted by him are given below. (1) (I) (II) (III) (IV) Sodium hydroxide is in the form of pellets. It dissolves in water readily. The beaker appears cold when touched from outside. The red litmus paper turns blue when dipped into the solution. The correct observations are: (A) I, II and III

21 (B) II, III and IV (C) III, IV and I (D) I, II and IV Q28 Read the following statements: (1) I. When a red litmus paper is dipped into reaction mixture of a saponification reaction, it turns blue and the reaction is exothermic. II. When a blue litmus paper is dipped into reaction mixture of a saponification reaction, its colour does not change and the reaction is exothermic. III. When a red litmus paper is dipped into reaction mixture of a saponification reaction, its colour does not change and the reaction is endothermic. IV. When a blue litmus paper is dipped into reaction mixture of a saponification reaction, its colour does not change and the reaction is endothermic. Which of the above statements are correct? (A) I and II (B) II and III (C) III and IV (D) I and IV Q29 Hard water required for an experiment is not available in a school laboratory. However, following salts are available in the laboratory. Select the salts which may be dissolved in water to make it hard for the experiment. (1) (1) Calcium Sulphate (2) Sodium Sulphate (3) Calcium Chloride (4) Potassium Sulphate (5) Sodium Hydrogen Carbonate (6) Magnesium Chloride (A) 1, 2 and 4 (B) 1,3 and 6 (C) 3,5 and 6 (D) 2,4 and 5 Q30 A student focused the image of a distant object using a device X on a while screen S as shown in the figure. If the distance of the screen from the device is 40 cm, select the correct statement about the device. (1)

22 (A) The device X is a convex lens of focal length 20 cm. (B) The device X is a concave mirror of focal length 40 cm. (C) The device X is a convex mirror of radius of curvature 40 cm. (D) The device X is a convex lens of focal length 40 cm. Q31 A student obtained a sharp image of a burning candle, placed at the farther end of a laboratory table, on a screen using a concave mirror. For getting better value of focal length of the mirror, the subject teacher suggested him for focusing a well illuminated distant object. What should the student do? (1) (A) He should move the mirror away from the screen. (B) He should move the mirror slightly towards the screen. (C) He should move the mirror as well as the screen towards the newly selected object. (D) He should move only the screen towards the newly selected object. Q32 After tracing the path of rays of light through a glass slab for three different angles of incidence, a student measured the corresponding values angle of refraction r and angle of emergence e and recorded them in the table given below: (1) The correct observations are: (A) I and II (B) II and III (C) I and III (D) I, II and III

23 Q33 Select from the following the best set-up for tracing the path of a ray of light through a rectangular glass slab: (1) (A) I (B) II (C) III (D) IV Q34 While performing the experiment to trace the path of a ray of light passing through a glass prism, four students marked the incident ray and the emergent ray in their diagrams in the manner shown below. (1)

24 (A) I (B) II (C) III (D) IV Q35 In an experiment to trace the path of a ray of light through a glass prism for different values of angle of incidence a student would find that the emergent ray: (1) (A) Is parallel to the incident ray (B) Perpendicular to the incident ray (C) Is parallel to the refracted ray (D) Bends at an angle to the direction of incident ray Q36 Study the following ray diagrams: (1)

25 The diagrams showing the correct path of the ray after passing through the lens are: (A) II and III only (B) I and II only (C) I, II and III (D) I, II and IV Q37 Out of the five incident rays shown in the figure find the three rays that are obeying the laws of refraction and may be used for locating the position of image formed by a convex lens: (A) 1,2 and 3 (B) 2,3 and 4 (C) 3,4 and 5 (D) 1,2 and 4 Q38 A student after observing a slide showing different stages of binary fission in Amoeba draws the following diagrams. However these diagrams are not in proper sequence: The correct sequence is: (A) I,V,IV,III,II (B) I,III,IV,V,II (C) I,V,III,IV,II (D) I,IV,V,III,II Q39 Select the correct statements for the process of budding in yeast: (1) I. A bud arises from a particular region on a parent body.

26 II. A parent cell divides into two daughter cells, here the parental identity is lost. III. Before detaching from the parent body a bud may form another bud. IV. A bud when detaches from the parent body grows into a new individual. (A) I, II and III (B) II, III and IV (C) III, IV and I (D) IV, I and II Q40 Study the different conclusions drawn by students of a class on the basis of observations of preserved/available specimens of plants and animals. (1) I. Potato and sweet potato are analogous organs in plants. II. Wings of insects and wings of birds are homologous organs in animals. III. Wings of insects and wings of bats are analogous organs in animals. IV. Thorns of citrus and tendrils of cucurbita are analogous organs in plants. The correct conclusions are: (A) I, and II (B) II and IV (C) I and III (D) III and IV Q41 You have potato, carrot, radish, sweet potato, tomato and ginger bought from the market in your jute bag. Identify two vegetables to represent the correct homologous structures. (1) (A) Potato and tomato (B) Carrot and tomato (C) Potato and sweet potato (D) Carrot and radish Q42 In the figure, the parts marked A, B and C are sequentially: (1) (A) Plumule,Radicle and Cotyledon (B) Radicle, Plumule and Cotyledon (C) Plumule, Cotyledon and Radicle (D) Radicle, Cotyledon and Plumule

27

28 CBSE CLASS X SCIENCE 2013 Section A Q1 There are 18 vertical columns in the modern periodic table and they are called as Groups. Q2 Speciation may be defined as an evolutionary process, which involves the formation of one or more species from an existing species. Q3 Biodegradable wastes can be properly recycled for future use. If biodegradable and non biodegradable wastes are discarded in the same dustbin, then the nonbiodegradable waste will make the biodegradable waste unfit for recycling. It will also interfere in the process of recycling. Q4 In sexually reproducing parents, the germ cells have half the number of chromosomes and DNA as compared to the other non reproductive cells of the body. When these germ cells, i.e. sperms and ova combine with each other at the time of sexual reproduction, the original chromosome number is attained in the zygote. This zygote further develops into a complete individual having the same chromosome number as present in the parents.

29 Q5 EF is the incident ray and GH is the emergent ray which is parallel to the incident ray. Q6 Some of the ways to make people realize that the improper disposal of waste is harmful to the environment are: Q7 (a) Improper disposal of waste will serve as a breeding ground for mosquitoes and will create favorable conditions for the spread of various diseases. (b) Improper disposal of waste will release harmful gases in the environment. It will make the environment unclean and unhygienic for normal living of the organisms. (c) The waste will flow to water bodies along with the rain water and become a threat to aquatic organisms.

30 Two advantages associated with water harvesting at community level are: (a) It will reduce the overexploitation of water resources. (b) It also helps in mitigation of droughts and floods. Q8 The product formed is: H 2 SO 4 is a dehydrating agent. So, ethanol undergoes dehydration i.e., loses a water molecule to form ethane. Q9 Homologous series of carbon compounds are so called because in such a series of compounds, the same functional group dictates the properties of the carbon compound regardless of the length of the carbon chain. The two consecutive members of a homologous series are CH 3 OH and C 2 H 5 OH (belong to alcohol)

31 Q10 Q11 (i) 19K has one electron in the outermost shell and its electronic configuration is (ii) 4Be and 20 Ca belongs to same group i.e. Group-2. Electronic configuration : 4Be Ca The number of electrons in the outermost shell of 4 Be and 20 Ca is same hence they belong to the same shell. (iii) 9F and 4 Be belongs to the same period, Period 2. Electronic configuration : 9F 2 7 4Be 2 2 4Be has bigger atomic size then 9 F because the atomic radius decreases as we move from left to right due to increase in nuclear charge which tends to pull the electrons closer to the nucleus and hence size of F reduces. In the modern periodic table there are total of 7 periods. The valency of an element is determined by the number of valence electrons present in the outermost shell of its atom. On moving from left to right in a period the valence electrons increase in s and p-blocks. In going from left to right the valency changes from positive to negative. On moving from left to right in a period metallic character decreases as nuclear charge on valence shell electrons increases so, tendency to lose electrons decreases and hence metallic character decreases. Down the group, valency remains the same as it depends upon valency shell electrons which remain the same on moving down the group and atomic size increases because a new shell is added. Q12 In Planaria, any part of the body which gets cut is capable of regeneration or developing into a complete organism. Regeneration is carried out by specialized cells. These cells proliferate and make large number of cells. From this mass of cells, different cells undergo changes to become various cell types and tissues. These changes take place in an organized sequence referred to as development.

32 Q13 Sexually transmitted diseases by virus Genital Herpes by herpes simplex virus and AIDS by HIV. Sexually transmitted diseases by bacteria Gonorrhea by Nisseria gonorrhoeae and Syphilis by Trepanoma pallidum Prevention of transmission of STD s Having sex with infected or any unknown person should be avoided. Sharing of needles, syringes etc. must be prohibited.

33 Q14 The surgical and dental instruments should be sterilized properly before use. Avoid blood transfusion from infected person. Blood should be tested before transfusion. Adequate medical treatment should be provided to the pregnant woman to protect the child from getting infected. Acquired traits The acquired traits are the traits which are experienced by an individual during his life time. It involves changes in non-reproductive tissues (or somatic cells), which cannot be passed on to the germ cells or progeny. Example learning of dance, cut marks etc. Inherited traits Inherited traits are distinguishing qualities or characteristics which one acquires from the ancestors. These involve change in the DNA. Hence, they are transmitted to the progeny. Example: height, eye, skin color etc. Q15 In human beings, the females have two X chromosomes and the males have one X and one Y chromosome. Therefore, the females are XX and the males are XY. At the time of mating, large number of sperms is ejaculated from the male reproductive organ (penis), into the female reproductive organ i.e. vagina. They travel towards the fallopian tubes, where only one sperm meets with the egg. The process of fusion of the sperm and ovum is called fertilization. The sperm has either X or Y chromosome and egg has only X chromosome. So if sperm carrying Y chromosome fuses with egg the newly born child will be made and if sperm carrying X chromosome fuses with the egg the newly born child will be female. There is equal change of fusion of either X or Y chromosome with the egg so we can say that the sex of new born child is a matter of change and none of the parent is responsible for it. Sex determination in human is shown below:

34 Q16 (i) Rear view mirrors : Convex mirrors Reason: (a) Image is formed virtual and erect always. (b) Image formed is always diminished in size, so it covers large view area. (ii) Shaving mirrors: Concave mirrors Reason: (a) Image formed is larger in size so as to see clearly details of the object. (b) Image formed is virtual and erect when object is placed close to the mirror. Q17 We have height of object, h 1 = 6 cm, focal length of lens, f = -5 cm and object distance, u = - 10 cm Using lens formula, we have

35 Thus the image will be formed in front of the lens at a distance of 3.33 cm from the lens, virtual and erect of size 2 cm. Q18 Differences in colors of the sun at sunrise/sunset and at noon are as follows: (i) Sunrise/sunset : Reddish in colour Reason : Sunlight travels longer distance at this time of the day, so the short wavelength colors get scattered away and the sunlight is left with only longer wavelength lights which is reddish or orange. So the sun appears reddish in colour. (ii) Noon : while in colour Q19 Reason: Sunrays travel shorter distance at noon and contains all the wavelengths of light which combine to form white colour. This makes the colour of sun white. Ecosystem is a self sustaining system where the biotic and abiotic organisms of various communities interact with each other. (a) The two components of the ecosystem are Biotic and Abiotic. Biotic system consists of all the living organisms of particular area like humans, animals etc and the nonliving or abiotic component consists of air, mineral soil, water and sunlight. (b) Ponds are the example of natural ecosystem whereas the aquarium is an example of artificial ecosystem. Ponds do not need to be cleaned but aquarium needs to be cleaned. This is because aquarium does not contain soil and decomposing bacteria which helps in degrading complex organic substance into simple inorganic substance. But pond has this facility. Therefore, it does not need to be cleaned.

36 Q20 (a) Molecules having same molecular formula but different structural formula are known as isomers. (b) Two possible isomers of the compound with molecular formula C 3 H 6 O : (c) Electron dot structure : Q21 (c) In case of sexual reproduction, there is marked variation between the parent and offspring due to the following reasons : 1. The male and female gametes are formed by meiotic division which allows crossing over and recombination. This generates variation in the genes of offspring.

37 Q22 Q23 2. Two parents are involved who are different from each other. The fusion of their gamete would produce a distinct individual. (a) A Stigma, Function The stigma is a sticky surface where the pollen lands and later germinates B Pollen tube, Function It carries the pollen to the egg cell for fertilization C Egg cell, Function It fuses with the male gamete and leads to the formation of zygote. (b) Role of gametes The gametes play an important role in the sexually reproducing organisms as they carry the entire genetic information of the organism. These gametes upon fusion result in the formation of zygote, which develops into a new individual. Any deformation in the gametes will lead to the deformity in the newly formed offspring. Role of zygote Zygote is the diploid cell formed by the fusion of male and female gametes during fertilization in sexual reproduction. Zygote is the first stage in the development process of an organism and it contains all the genetic information of both the parents, essential for the growth of the new organism. (a) Laws of refraction There are two laws of refraction. First law of refraction The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant. This is known as Snell s law. Mathematically, it can be given as follows: sin i sin r = n ab Here, n ab is the relative refractive index of medium a with respect to medium b. Second law of refraction The incident ray, the refracted ray, and the normal to the interface of two media at the point of incidence all lie in the same plane. If the light ray goes from medium 1 to 2 then the refractive index of medium 1 with respect to medium 2 is, speed of light in medium 2 n 12 = = v 2 where, v 1 and v 2 are the speeds of light in medium 1 and 2 speed of light in medium 1 v 1 respectively. (b) Given : Refractive index of water, n w = 4/3 and Refractive index of glass, n g = 3/2

38 Speed of light in glass, v g = 2 x 10 8 m/s Q24 (a) The person is suffering from Hypermetropia i.e. Far-sightedness. Hypermetropia is caused due to: (i) (ii) The focal length of the eye lens is too long Decrease in the length of the eyeball This defect can be corrected using convex lens of appropriate focal length.

39 (b) Eye donation : Our eye can live even after our death, so by donating our eyes, we can give vision to any blind person and make him see. By giving such advertisement in newspaper we can aware more people for this noble cause and raise the number of donations for blind people. Section B Q25 (D) When 2 ml acetic acid is taken in a dry test tube and a pinch of sodium hydrogen carbonate is added to it, a colourless and odourless gas evolves with a brisk effervescence which is CO 2. When CO 2 is passed through lime water it turns lime water milky. CO 2 also extinguishes the burning splinter when it is brought near it. Q26 (A) The acetic acid dissolves readily in water. Q27 (D)

40 Sodium hydroxide is in the form of pallets and it readily dissolves in water to form a solution. As it is basic in nature, it turns red litmus paper blue. Q28 (A) The saponification reaction is exothermic and the soap solution is basic in nature so it turns red litmus paper into blue. When a blue litmus paper is dipped, its colour does not change. Q29 (B) Hard water contains Ca 2+ and Mg 2+ ions. So the salts that can be added to water to make it hard are calcium sulphate, calcium chloride and magnesium chloride. Q30 (D) As the light rays are passing through the device X and the image formed is real thus the given device is a convex lens. Secondly, we are getting a focused image at the screen so the focus length of the lens is 40 cm. Q31 (B) As the image distance is increased, the object distance would decrease and thus the mirror-screen distance should be decreased. Therefore, the mirror should be moved towards the screen. Q32 (D) For light rays passing through a glass slab, the following conditions should hold true: (2) Also, with the increase in incident angle, the refracted angle also increases. Both of these conditions are satisfied in all the three observations. Q33 (A)

41 The best set up is given in figure (i). The incoming light should not fall perpendicularly as the light will emerge straight and refraction cannot be traced. The light rays should not be very close or far from the normal as the emergent rays are difficult to trace. Q34 (C) When light goes from rarer medium to denser medium, it bends towards the normal and vice-versa. This condition is fulfilled in figure (III). Q35 (D) As the light gets refracted two times at different angles. The emergent ray bends at an angle top the direction of incident ray. Q36 (C) Ray diagrams (I), (II) and (III) are correct. The light rays passing through the optical centre of lens remain undeflected. The light rays parallel to principal axis passes through the second focus of the lens The light rays passing through the first focus become parallel to the principal axis after passing through the lens. Q37 (B) Rays (2),(3) and (4) obey the laws of refraction. Ray parallel to the principal axis passes through the second focus of the lens. Ray passing through the optical centre goes undeflected. Ray passing through the first focus of the lens goes parallel to the principal axis, Q38 None of the given answer choices are CORRECT. Consult your teacher. The correct sequence should be I, II, III, IV, V.

42 Q39 (C) Yeast reproduces asexually by the process of budding. Budding is a type of asexual reproduction in which a new organism is formed from a bud of an existing organism. A small bud is formed at a specific position on the parallel cell. The nucleus of parent cells splits and a part of it enters inside the newly formed bud. The bud develops into a new cell or daughter organism. The new organism remains attached to the parent organism till it gets matured. After attaining maturity it separates from the parent body. Q40 (C) Analogous organs are those which do not share a common ancestry but perform common function. Hence, wings of insects and wings of bats are analogous organs in animals. Hence, potato and sweet potato are analogous organs in plants. Q41 (D) Homologous structures are similar in origin but perform different functions. Carrot and radish are underground roots. So, they represent the correct Homologous structures. Q42 (A) In the figure, the parts marked A, B, and C are Plumule, Radicle and Cotyledon respectively.

43 Class X CBSE 2014 Science General Instructions: (i) (ii) (iii) (iv) (v) (vi) (vii) (viii) The question paper comprises of two Sections, A and B. You are to attempt both the section. All questions are compulsory. All question of Section A and all questions of Section B are to be attempted separately. Question numbers 1 to 3 in Sections A are one mark questions. These are to be answered in one word or in one sentence. Question numbers 4 to 7 in Section A are two marks questions. These are to be answered in about 30 words each. Question number 8 to 19 in Section A are three marks questions. These are to be answered on about 50 words each. Question numbers 20 to 24 in Section A are five marks questions. These are to be answered in about 70 words each. Question numbers 25 to 42 in Section B are multiple choice questions based on practical skills. Each question is a one mark question. You are to select one most appropriate response out of the four provided to you. Section A 1. Write the number of vertical columns in the modern periodic table. What are those columns called? Section B 2. Give the respective scientific terms used for studying: (i) The mechanism by which variations are created and inherited and (ii) The development of new type of organisms from the existing ones. 3. Water is a valuable resource. List two ways that you would suggest every family member to save this resource. 4. List four advantages of vegetative propagation.

44 5. Draw a ray diagram to show the path of the reflected ray corresponding to an incident ray which is directed parallel to the principal axis of a convex mirror. Mark on it the angle of incident and the angle of reflection. 6. Why is Government of India imposing a ban on the use of polythene bags? Suggest two alternatives to these bags and explain how this ban is likely to improve the environment. 7. What is meant by biodiversity? List two advantages of conserving forest and wild life. 8. State the meaning of functional group in a carbon compound. Write the functional group present in (i) ethanol and (ii) ethanoic acid and also draw their structures. 9. Write the name and general formula of a chain of hydrocarbons in which an addition reaction with hydrogen can take place. Stating the essential conditions required for an addition reaction to occur, write the chemical equation giving the name of the reactant and the product of such a reaction. 10. Based on the group valency of elements state the formula for the following giving justification for each: (i) Oxides of 1 st group elements. (ii) Halides of the elements of group 13, and (iii) Compounds formed when an element of group 2 combines with, an element of group (a) Define the following terms: (i) Valency (ii) Atomic size (b) How do the valency and the atomic size of the elements vary while going from left to right along a period in the modern periodic table? 12. Draw diagrams to explain the regeneration that takes place in each of the body parts of planaria when its body is out into pieces. Name any other organism in which a similar process can be observed. 13. List any four methods of contraception used by humans. How does their use have a direct effect on the health and prosperity of a family? 14. (a) Give the evidence that the birds have evolved from reptiles. (b) Insects, octopus, planaria and vertebrates possess eyes. Can we group these animals together on the basis of eyes that they possess? Justify your answer giving reason. 15. A cross was made between pure breeding pea plants one with round and green seeds and the other with wrinkled and yellow seeds. (a) Write the phenotype of F 1 progeny. Give reason for your answer. (b) Write the different types of F 2 progeny obtained along with their ratio when F 1 progeny was selfed.

45 16. A spherical mirror produces an image of magnification -1 on a screen placed at a distance of 50 cm from the mirror. (a) Write the type of mirror. (b) Find the distance of the image from the object. (c) What is the focal length of the mirror? (d) Draw the ray diagram to show the image formation in this case. 17. State the laws of refraction of light. If the speed of light in vacuum is 3X10 8 ms -1, find the speed of light in a medium of absolute refractive index Explain giving reason why the sky appears blue to an observer from the surface of the earth? What will the color of the sky be for an astronaut staying in the international space station orbiting the earth? Justify your answer giving reason. 19. Our food grains such as wheat and rice, the vegetables and fruits and even meat are found to contain varying amounts of pesticide residues. State the reason to explain how and why it happens? 20. State the reason why carbon can neither form C 4+ cations nor C 4- anions but forms covalent compound. Also state the reason to explain why covalent compounds: (i) (ii) Are bad conductors of electricity. Have low melting and boiling points. 21. (a) Give one example each of a unisexual and a bisexual flower. (b) Mention the changes a flower undergoes after fertilisation. (c) How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals? 22. (a) Name the respective part of human female reproductive system: (i) that produces eggs, (ii) Where fusion of eggs and sperm takes place, and (iii) Where zygote gets implanted. (b) Describe in brief what happens to the zygote after it gets implanted. 23. A student wants to project the image of a candle flame on the walls of school laboratory by using a lens:

46 (a) Which type of lens should be use and why? (b) At what distance in terms of focal length F of the lens should be place the candle flame so as to get (i) a magnified, and (ii) a diminished imaged respectively on the wall? (c) Draw ray diagram to show the formation of the image in each case? 24. (a) List three common refractive defects of vision. Suggest the way of correcting these defects. (b) About 45 lac people in the developing countries are suffering from corneal blindness. About 30 lac children below the age of 12 years suffering from this defect can be cured by replacing the defective cornea with the cornea of a donated eye. How and why can students of your age involve themselves to create awareness about this fact among people? Section C 25. When you add about 2 ml of acetic acid to a test tube containing an equal amount of distilled water and leave the test tube to settle shaking its contents, what will you observe in the test tube after about 5 minutes? (A) A white precipitate settling at its bottom. (B) A clear colourless solution (C) A layer of water over the layer of acetic acid (D) A layer of acetic acid over the layer of water 26. A student adds a few drops of ethanoic acid to test tubes X, Y and Z containing aqueous solutions of sodium chloride, sodium hydroxide and sodium carbonate, respectively. If he now brings a burning splinter near the mouth of the test tubes immediately after adding ethanoic acid in each one of them, in which of the test tube or test tubes the flame will be extinguished? (A) X and Y (B) Y and Z (C) X and Y (D) only Z 27. In order to study saponification reaction, we first prepare 20% solution of sodium hydroxide. If we record the temperature of this solution just after adding sodium hydroxide flakes to water and also test its nature using litmus, it may be concluded that the process of making this solution is (A) exothermic and the solution is alkaline (B) endothermic and the solution is alkaline (C) endothermic and the solution is acidic

47 (D) exothermic and the solution is acidic 28. While studying saponification reaction for the preparation of soap, a teacher suggested to a student to add a small quantity of common salt to the reaction mixture. The function of common salt in this reaction is to (A) reduce the alkalinity of the soap (B) reduce the acidity of the soap (C) enhance precipitation of soap (D) favour precipitation of soap 29. A student takes about 6 ml of distilled water in each of the four test tubes, P, Q, R and S. He then dissolved an equal amount of four different salts namely, sodium chloride in P potassium chloride in Q, calcium chloride in R and magnesium chloride in S. Next, he then adds 10 drops of soap solution to each test tube shakes its contents. The test tubes in which scum (insoluble substance) is formed with soap are: (A) P and Q (B) Q and R (C) R and S (D) Q and S 30. A student has obtained the image of a distant object with a concave mirror to determine its focal length. If he has selected a well illuminated red building as object, which of the following correctly describes the features of the image formed? (A) Virtual, inverted and diminished image in red shade (B) Real, erect and diminished image in pink shade (C) Real, inverted and diminished image in red shade (D) Virtual, erect and enlarged image in red shade 31. A student has obtained an image of a distant on a screen to determine the focal length F 1 of the given lens. His teacher, after checking the image, gave him another lens of focal length F 2 and asked him to focus the same object on the same screen. The student found that to obtain a sharp image, he has to move the lens away from the screen. From this finding, we may conclude that both the lenses given to the student were: (A) Concave and F 1 < F 2

48 (B) Convex and F 1 < F 2 (C) Convex and F 1 > F 2 (D) Concave and F 1 > F Study the following four experimental set-ups I, II, III and IV for the experiment, "To trace the path of a ray of light through a rectangular glass slab." Which of the marked set-ups is likely to give best results (P1 and P2 are the positions of pins fixed on the incident ray)? (A) I (B) II (C) III (D) IV 33. On the basis of the experiment, "To trace the path of a ray of light through a rectangular glass slab", students of a class arrived at which one of the following conclusions? (A) Angle of incidence is greater than the angle of emergence. (B) Angle of emergence is smaller than the angle of refraction. (C) Emergent ray is parallel to the refracted ray. (D) Incident ray and emergent ray are parallel to each other.

49 34. The path of a ray of light passing through a glass prism is shown below: In this diagram, the angle of prism, angle of incidence, angle of emergence and angle of deviation, respectively, have been represented by: (A) O, Y, Z and N (B) P, Y, M and Z (C) O, X, M and Z (D) P, X, Z and N. 35. A student is observing a diagram showing the path of a ray of light passing through a glass prism. He would find that for all angles of incidence the ray of light bends: (A) towards the normal while entering the prism and away from the normal while emerging from the prism (B) away from the normal while entering the prism and towards the normal while emerging from the prism (C) away from the normal while entering as well as while emerging from the prism (D) towards the normal while entering as well as while emerging from the prism 36. A student was asked by his teacher to find the image distance for various object distance in case of a given convex lens. He performed the experiment with all precautions and noted down his observations in the following table:

50 After checking the observations table the teacher pointed out that there is a mistake in recording the image distance in one of the observations. Find the serial number of the observations having faulty image distance. (A) 2 (B) 3 (C) 5 (D) A student has obtained a magnified image of a flame on a screen using a convex lens. To draw the corresponding ray diagram to show the image formation, which of the following two rays whose paths after refraction are shown, should he select? (A) I and II (B) II and III

51 (C) III and IV (D) I and III 38. Study the following diagrams showing various stages of binary fission in Amoeba: The correct sequence of these diagrams should be: (A) I, IV, III, II, V (B) I, III, IV, II, V (C) I, II, IV, III, V (D) I, II, III, IV, V 39. Identify the figures showing the process of budding in yeast. (A) I, II and III (B) II, III and IV (C) I, II and IV (D) III, IV and I 40. Which one of the following pairs of vegetables is an example of homologous structures? (A) Potato and sweet potato (B) Carrot and radish (C) Carrot and tomato (D) Tomato and radish 41. Four students P, Q, R and S differently reported the following set of organs to be analogous: P. Forelimb of a frog and forelimb of a lizard Q. Forelimb of a bird and forelimb of a human

52 R. Wings of a parrot and wings of a butterfly S. Wings of a bird and wings of a bat The two students who have reported correctly are: (A) P and Q (B) Q and R (C) R and S (D) P and S 42. You are asked by your teacher to study the different parts of an embryo of a gram seed. Given below are the steps to be followed for the experiment: I. Soak the gram seeds in plain water and keep them overnight. II. Cut open a soaked seed and observe its different parts. III. Take some dry gram seeds in a petri dish. IV. Drain the excess water. V. Cover the soaked seeds with a wet cotton cloth and leave them for a day. The correct sequence of these steps is : (A) III, I, V, IV, II (B) III, I, II, IV, V (C) III, IV, V, I, II (D) III, I, IV, V, II

53

54 CBSE-CLASS -X-Science Section A 1. There are 18 vertical columns in the modern periodic table and these are known as groups. Section B 2. (i) Genetics is the study of mechanism by which variations are created and inherited. (ii) Evolution is used for studying the development of new types of organisms from the existing ones. 3. Two ways of saving water: a. Turning-off the taps when not in use b. Checking the leaking water pipelines and getting them repaired 4. Vegetative propagation is an asexual mode of reproduction. It is the ability of the plants to reproduce by producing new plants from the vegetative parts such as leaf, stem, or roots under favourable conditions. Advantages of vegetative propagation: a. Only one parent is required, which eliminates the need for special mechanisms (pollination). b. Many plants are able to tide over unfavourable conditions because of the presence of vegetative reproductive parts like the tubers, corm, bulbs, etc. c. Plants that do not produce seeds are propagated by this method. For example: Sugar-cane, Potato, etc. d. Vegetative propagation is a cheaper, easier and rapid method of propagation in plants than growing them from their seeds. For example, when grown from their seeds, lilies grow very slowly and take 4 to 7 years to develop flowers, but flowers are produced only in a year or two when grown vegetatively. e. The trait (character) of the parent plant is preserved and the offsprings are genetically identical.

55 (Any four advantages can be written) Government of India is imposing a ban on the use of polythene bags because they cannot be degraded naturally by the action of microorganisms. Because of their nonbiodegradability, they stay in the soil for a long time and continue to poison it with toxic by-products that keep leaching from them. Also, they do not allow water to seep in, as they are waterproof. These polythene bags, when accidentally eaten by stray animals, can harm them and can even lead to their death. Jute and cloth bags can be used in place of polythene bags. The advantages of using cloth and jute bags are as follows: a. They are environment-friendly as they are biodegradable. b. They are renewable and can be easily recycled. c. They have more strength than polythene bags because they are thick and can be used again and again. Thus, using jute and cloth bags will helps to reduce pollution 7. Biodiversity refers to the variety of living organisms present in the given ecosystem. It includes all the marine and terrestrial organisms. The biodiversity of an area is measured by counting the number of species found in that particular area. Advantages of conserving forest: (i) It prevents soil erosion and floods. (ii) It helps to maintain the water cycle. (iii) It produces huge amounts of raw materials for the industries.

56 (Any of the two advantages can be written) Advantages of conserving wildlife: (i) It protects the endangered species. (ii) It preserves different kinds of species and thus, maintains the species diversity. (iii) It helps in maintaining the ecological balance that is required for supporting life. (Any of the two advantages can be written) 8. Definition: Functional group is an atom or a group of atoms that is bonded to a carbon chain. It defines the chemical property of the organic compound. 9. Name and general formula of hydrocarbons undergoing addition reaction with hydrogen: Essential conditions required for the addition reaction to occur: o o Multiple bonds (double and triple bonds) must be present between carbon atoms in the chain of hydrocarbon. Addition of hydrogen should be carried out in the presence of catalyst such as nickel or platinum. Chemical Equation:

57 10. (i) Valency of group 1 elements: 1 Valency of oxygen: 2 Oxides of group 1 elements: Formula of the oxides of group 1 is M 2 O, where M is the group 1 element and O is oxygen. (ii) Valency of group 13 elements: 3 Valency of halogens: 1 Halides of group 13 elements: Formula of the halides of group 13 is MX 3, where M is the group 13 element and X is halogen. (iii) Valency of group 2 elements: 2 Valency of group 16 elements: 2 Compounds of group 2 and group 16 elements: Formula of the compounds of group 2 and 16 is MN, where M is the group 2 element and N is the group 16 element. 11. a. (i) Valency: The combining power or the combining capacity of an atom is called its valency. Valency of an atom is simply equal to the number of electrons gained, lost or

58 shared by an atom to achieve the nearest noble gas configuration. (ii) Atomic size: Atomic size or atomic radius is the distance between the centre of the nucleus and the outermost shell of an isolated atom. b. Variation in valency On moving from left to right in the periodic table, valency increases up to 4 and then decreases. a. The electrons present in the last shell determine the valency of a particular element. b. If the number of valence electrons is less than or equal to 4, valency = number of valence electrons c. If the number of valence electrons is more than 4, valency = 8 - number of valence electrons Variation in atomic size: Atomic size decreases along a period. This is because on moving across a period, the number of valence shells remains the same and the electrons increase by one unit. As a result, the nuclear charge increases and thus, the atomic radius decreases. 12. Planaria is a type of flatworm. It has the amazing capacity to regenerate its lost body part. When the flatworm is cut horizontally, separating the head from the tail, the tail will regenerate the lost head and the head will regenerate the lost tail. This process is known as regeneration. The diagram illustrating the process of regeneration in Planaria is given below Regeneration is one of the methods of asexual reproduction, which can be observed in Hydra also.

59 13. The following are the four methods of contraception used by humans: (i) Natural method: It involves avoiding the chances of meeting of the sperm and the ovum. In this method, the sexual act is avoided from day 10th to day 17th of the menstrual cycle because during this period, ovulation is expected; therefore, the chances of fertilisation are very high. (ii) Barrier method: In this method, fertilisation of the ovum and sperm is prevented with the help of barriers. Barriers are available for both males and females. Condoms, which are made of thin rubber, are used to cover the penis in males and the vagina in females. (iii) Oral contraceptives: In this method, tablets or drugs are taken orally. These contain small doses of hormones that prevent the release of eggs, thus preventing fertilisation. (iv) Implants and surgical methods: Contraceptive devices such as the loop or copper-t are placed in the uterus to prevent pregnancy. Some surgical methods can also be used to block the gamete transfer. In vasectomy, the vas deferens is blocked to prevent the transfer of sperms. Similarly, in tubectomy, the fallopian tubes of the female can be blocked so that the egg does not reach the uterus. Effects of contraception on the health and prosperity of a family: (i) It helps in preventing unwanted pregnancies. (ii) It prevents the chances of frequent pregnancies, which otherwise affect the health of females. (iii) It helps in family planning by controlling the number of children in a family, thus reducing the chances of poverty. (iv) It also reduces the chances of transmission of sexually transmitted diseases such as AIDS. In this way, birth control methods play an important role in the health and prosperity of a family 14. (a) Fossils provide evidence of evolution. A fossil bird called Archaeopteryx, which lived in the Late Jurassic Period around million years ago, had feathered wings like that of birds and a long bony tail, jaws with sharp teeth and various skeletal features like that of reptiles. Thus, Archaeopteryx is considered a connecting link between reptiles and birds. Some dinosaurs had feathers that provide them insulation in cold weather; however, they could not fly using those feathers. Birds seem to have later used feathers to fly. This, of course, means that birds are very closely related to reptiles because dinosaurs were reptiles. Hence, it suggests that birds have evolved from reptiles.

60 (b) While making groups, we need to decide the characteristics that are responsible for the more fundamental differences among organisms. The characteristics that account for the broadest divisions among living organisms should be independent of any other characteristics in their effects on the forms and structural functions of organisms like cellularity, mode of nutrition and nature of cell. Insects, octopus and planaria are invertebrates; they cannot be grouped together with vertebrates, as they lack an internal skeleton with a backbone. Also, all of them belong to different phyla on the basis of different characteristics they possess. Just on the basis of one characteristic, i.e., presence of eyes, these organisms cannot be grouped together. 15. (a) The cross was made between round, green seeds and wrinkled, yellow seeds. In the given cross, two traits were taken into account, which is a dihybrid cross. Yellow colour and round shape is dominant over green colour and wrinkled shape. The above cross shows round and yellow seeds in the F1 generation. It occurs because dominant traits (round and yellow) express itself, whereas recessive traits (wrinkled and green) get suppressed. (b) On selfing of F1 generation

61 Phenotypic ratio 9:3:3:1 Round yellow 9 Round green 3 Wrinkled yellow 3 Wrinkled green (a) As magnification is negative, the image formed is real. Hence, it is a concave mirror. v (b) m = = 1 u u = v = 50 cm Distance of the image from the object = = 100 cm (c) By using mirror formula: f = 25 cm (d)

62 17. (a) There are two laws of refraction: First law of refraction: The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant. This is known as Snell s law. Mathematically, it can be expressed as: Here, n12 is the relative refractive index of medium 1 with respect to medium 2. Second law of refraction: The incident ray, the refracted ray and the normal to the interface of two media at the point of incidence lie on the same plane. If a light ray goes from medium 1 to medium 2, then the refractive index of medium 1 with respect to medium 2 is expressed as: Here, v1 and v2 are the speeds of light in medium 1 and medium 2, respectively. (B) Given: Speed of light in vacuum = ms 1 Refractive index of the medium: Hence, the speed of light in the medium of refractive index 1.5 is m/s.

63 18. Sunlight reaches the Earth's atmosphere and is scattered in all directions by the gases and particles in the air. Blue light is scattered more than the other colours because it has the shortest wavelength. This is why the sky appears blue to an observer from the surface of the Earth. For an astronaut staying in the international space station orbiting the Earth, the colour of the sky will be black because the light reaching it does not scatter. 19. A large number of pesticides and chemicals are used to protect our crops from pests and diseases. Some of these chemicals are washed down into the soil, while some enter in the water bodies. From the soil, they are absorbed by plants along with water and minerals; and from water bodies, they are taken up by aquatic plants and animals. This is how these chemicals enter the food chain. Because these chemicals cannot decompose, they accumulate progressively at each trophic level. As the food chain proceeds, the concentration of pesticides also increases. This increase in the concentration of harmful chemicals with each step of the food chain is called biomagnification. That is why food grains, such as wheat and rice, vegetables, fruits and even meat are found to contain pesticide residue. 20. Atomic number of carbon is six. This means that it has four electrons in its outermost shell and it needs four more electrons to attain noble gas electronic configuration. It does not form C 4+ cation, as the removal of four valence electrons will require a huge amount of energy. The cation formed will have six protons and two electrons. This makes it highly unstable. Carbon is unable to form C 4 anion as its nucleus with six protons will not be able to hold ten electrons. Thus, carbon achieves noble gas electronic configuration by sharing its four electrons with other elements, i.e. it forms covalent compounds. (i) Covalent compounds are bad conductors of electricity due to lack of free electrons. (ii) Covalent compounds are formed by covalent bonds and it has been found that the intermolecular forces of attraction in covalent compounds are weak. Thus, their melting and boiling points are quite low. 21. (a) Unisexual flowers: Cucumber, pumpkin, water melon, papaya, etc. Bisexual flowers: Hibiscus, rose, lily, etc. (Any one example can be written). (b) Changes in a flower after fertilisation: The outer layers of the ovule become impervious and hard and function as a seed coat. An ovule with an embryo inside is called a seed.

64 The ovary enlarges and ripens to become a fruit. Other floral parts such as sepals, petals, stamens, styles and stigma may fall off. However, in some cases, they remain persistent in the fruit. (c) Deoxyribonucleic acid (DNA) copying is an essential part of reproduction, as it passes genetic information from parents to offspring. The reproducing cells produce a copy of their DNA through some chemical reactions and result in two copies of DNA. The copying of DNA always takes place along with the creation of additional cellular structure. This process is then followed by the division of a cell into two cells. In this way, the amount of DNA remains constant through each new generation. 22. (a) (i) Ovary (ii) Fallopian tube (iii) Uterus Diagram of the female reproductive system (a) The zygote formed after fertilisation in the fallopian tube is implanted in the uterus. It divides repeatedly to form a mass of cells known as embryo. This embryo gets attached to the inner layer of the uterine cavity, i.e., endometrium. It thickens every month and is supplied with blood to nourish the embryo. Soon it gets covered by rapidly dividing uterine cells. This leads to pregnancy.

65 Within a span of some months, the embryo starts developing limbs and begins to resemble a miniature human being. When all body parts of the embryo can be recognised, it becomes a foetus. When this foetus is fully developed, the mother gives birth to the baby. 23. (a) He should use a convex lens as it forms real images. (b) He should place the candle flame between F and 2F (the focus and centre of curvature of the lens) to get the magnified image on the wall while the diminished image is obtained when the object is located at a distance greater than 2F. (c) The ray diagram for the formation of the magnified image is shown below:

66 The ray diagram for the formation of the diminished image is shown below 24. (a) The three common refractive defects of vision are as follows: Myopia (short-sightedness): It is corrected by using spectacles having concave lenses of appropriate power. Hypermetropia (far-sightedness): It is corrected by using spectacles having convex lenses of appropriate power. Presbyopia: This defect is corrected using bifocal lenses of appropriate power in which the upper part consists of a concave lens (to correct myopia) and the lower part consists of a convex lens (to correct hypermetropia). (b) Eyes of a dead person can be donated to the person having corneal blindness. It will help him/her see the world. We can also register ourselves to eye donation camps who can preserve our eyes after our death and donate them to the needy. Section C 25. When acetic acid and distilled water are mixed, they form a clear solution because acetic acid is completely miscible with water. Hence, the correct option is B.

67 26. The chemical reactions in test tubes X, Y and Z can be written as: Test tube X: CH 3 COOH + NaCl No reaction Test tube Y: CH 3 COOH + NaOH CH 3 COONa + H 2 O Test tube Z: 2 CH 3 COOH + Na 2 CO 3 2 CH 3 COONa + CO 2 + H 2 O Thus, the flame will be extinguished when test tube Z is brought near a burning splinter due to evolution of carbon dioxide gas, which does not support combustion. Hence, the correct option is D. 27. Dissolution of sodium hydroxide in water evolves large amount of heat. Thus, it is an exothermic reaction. Since sodium hydroxide is a base, its solution in water will be alkaline when tested with litmus paper (red litmus turns blue). Hence, the correct option is A. 28. Common salt is added in saponification reaction, as it helps in the precipitation of soap by decreasing the solubility of soap. Hence, the correct option is D 29. Scum is formed by reaction of soap with calcium and magnesium salts in water. Test tubes R and S contain calcium chloride and magnesium chloride, respectively. Therefore, scum will be formed in these two tubes. Hence, the correct option is C. 30. To measure the focal length of the mirror, the object should be taken at infinity. Therefore, the image formed by the concave mirror would be real, inverted, diminished and red in shade.

68 Hence, the correct option is C. 31. The lens is convex, as it forms real image. As mentioned in the second case, the image distance (v) is increasing; hence, the object distance (u) is decreasing. The lens formula is For convex lens, object distance = -u Image distance = + v where F is the focal length of the lens. Therefore, F is lesser for the second lens of focal length F2. Hence, F1 > F2 Hence, the correct option is C. 32. Experiment II will give the best result because it has the largest angle of incidence, due to which the lateral displacement between the incident ray and emergent ray will be maximum. Hence, the correct option is B. 33. The correct conclusion is that the incident ray and emergent ray are always parallel to each other. Hence, the correct option is D. 34. O is the angle of prism. Angle of incidence is the angle made by the incident ray with the normal to the surface of the prism. Here, X represents the angle of incidence. Angle of emergence is the angle made by the emerging ray with the normal to the surface of the prism. Here, M represents the angle of emergence.

69 Angle of deviation is the angle made by the emerging ray with the incident ray. Here, Z represents the angle of deviation. Hence, the correct option is C. 35. When a ray of light enters a glass prism, it travels from a rarer medium to a denser medium. So, the ray of light bends towards the normal. When the ray of light emerges from the glass prism, it travels from a denser medium to a rarer medium. So, the ray of light bends away from the normal. Hence, the correct option is A. 36. Observation no. 3 is incorrect because the focal length of the lens in all other observations is 12 cm. In observation no. 3, the focal length comes out to be cm. Hence, the correct option is B. 37. A convex lens converges the refracting ray. Therefore, rays I and III represent the path of the refracting ray from a convex lens(converging lens). As rays II and IV show the refracting ray being diverged, the ray diagrams are incorrect. Hence, the correct option is D. 38. During binary fission, the nucleus of the parent cell elongates and divides initially. A constriction starts appearing on the cell membrane. It starts widening and finally divides the parent cell into two almost equal halves (daughter cells). The daughter cells are identical to the parent cell. Hence, the correct option is B.

70 39. III, IV and I show the process of budding in a yeast. During budding in a yeast, a single cell develops a protrusion wherein the nucleus divides to give rise to two daughter nuclei. One of the daughter nuclei migrates to the protrusion to form a bud. This bud then grows in size and may undergo budding while attached to the parent cell. Thus, budding results in a chain of cells. Hence, the correct option is D. 40. Homologous structures are similar in origin, but they perform different functions. Carrot and radish are underground roots, so they represent homologous structures. Hence, the correct option is B. 41. Organs that are different in origin but similar in function are known as analogous organs. Examples of analogous organs are: (i) Wings of a parrot and wings of a butterfly (ii) Wings of a bird and wings of a bat Thus, the two students who have reported correctly are R and S. Hence, the correct option is C. 42. First of all, take some dry gram seeds in a Petri dish. Now, soak the seeds in plain water and keep them overnight. Drain the excess water. After that, cover the soaked seeds with a wet cotton cloth and leave them for a day. Finally, cut open a soaked seed and observe its different parts. Hence, the correct option is D.

71

72 CBSE-CLAS X-SCIENCE-2015 The questions paper comprises two sections, A and B. You are to attempt both the sections. (ii) All questions are compulsory. (iii) There is no choice in any of the questions. (iv) All questions of Section A and all questions of Section B are to be attempted separately. (v) Question numbers 1 to 3 in Section A are one mark questions. These are to be answered in one word or one sentence. (vi) Question numbers 4 to 6 Section A are two marks questions. These are to be answered in about 30 words each. (vii) Question numbers 7 to 18 in Section A are three marks questions. There are to be answered in about 50 words each. (viii) Question numbers 19 to 24 in Section A are five marks questions. These are to be answered in about 70 words each. (ix) Question numbers 25 to 33 in Section B are multiple choice questions based on practical skills. Each question is a one mark question. You are to select one most appropriate response out of the four provided to you (x) Question numbers 34 to 36 in Section B are two marks questions based on practical skills. These are to be answered in brief. SECTION_A 1) Write the name and formula of the 2nd member of homologous series having general formula C n H 2n. 2) List two functions performed by the testis in human beings 3) What is the function of ozone in the upper atmosphere? 4) List four characteristics of the images formed by plane mirrors. 5) Why are forests considered "biodiversity hot spots"? List two ways in which an individual can contribute effectively to the management of forests and wildlife. 6) What is meant by "sustainable management"? Why is reuse considered better than recycling? 7) With the help of an example, explain the process of hydrogenation. Mention the essential conditions for the reaction and state the change in physical property with the formation of the product. 8) What is the difference between the molecules of soaps and detergents, chemically? Explain the cleansing action of soaps.

73 9) How many groups and periods are there in the modern periodic table? How do the atomic size and metallic character of elements vary as we move: (a) down a group and (b) from left to right in a period 10) From the following elements: 4Be; 9 F; 19 K; 20 Ca (i) Select the element having one electron is the outermost shell. (ii) Two elements of the same group. Write the formula of and mention the nature of the compound formed by the union of 19K and element X (2, 8, 7). 11) What is DNA copying? State its importance. 12) Explain budding in hydra with the help of labeled diagrams only. 13) List any four methods of contraception used by humans. How does their use have a direct effect on the health and prosperity of a family? 14) "We cannot pass on to our progeny the experiences and qualifications earned during our life time". Justify the statement giving reason and examples. 15) (i) Planaria, insects, octopus and vertebrates all have eyes. Can we group eyes of these animals together to establish a common evolutionary origin? Justify your answer. (ii) "Birds have evolved from reptiles" State evidence to prove the statement. 16) To construct a ray diagram we use two rays of light which are so chosen that it is easy to determine their directions after reflection from the mirror. Choose these two rays and state the path of these rays after reflection from a concave mirror. Use these two rays to find the nature and position of the image of an object placed at a distance of 15 cm from a concave mirror of focal length 10 cm. 17) With the help of a labeled diagram, explain why the sun appears reddish at the sun-rise and the sunset. 18) After the examinations Rakesh with his friends went on a picnic to a nearby park. All friends carried cooked food packed in plastic bags or plastic cans. After eating the food some friends collected the leftover food and plastic bags etc and planned to dispose them off by burning. Rakesh immediately checked them and suggested to segregate the leftover food and peels of fruits from the plastic materials and respectively dispose them off separately in the green and red dustbins placed in the corner of the park. (a) In your opinion, is burning plastic an ecofriendly method of waste disposal? Why? State the advantage of method suggested by Rakesh. (b) How can we contribute in maintaining the parks and roads neat and clean?

74 19) Explain why carbon forms compounds mainly by covalent bond. Explain in brief two main reasons for carbon forming a large number of compounds. Why does carbon form strong bonds with most other elements? 20) Write the functions of the following in human female reproductive system: Ovary, oviduct, uterus How does the embryo get nourishment inside the mother's body? Explain in brief. 21) How many pairs of chromosomes are present in human beings? Out of these how many are sex chromosomes? How many types of sex chromosomes are found in human beings? "The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it". Draw a flow chart showing determination of sex of a newborn to justify this statement. 22) (a) State the laws of refraction of light. Explain the term absolute refractive index of a medium and write an expression to relate it with the speed of light in vacuum. (b) The absolute refractive indices of two media 'A' and 'B' are 2.0 and 1.5 respectively. If the speed of light in medium 'B' is m/s, calculate the speed of light in: (i) vacuum, (ii) medium 'A'. 23) "A convex lens can form a magnified erect as well as magnified inverted image of an object placed in from of it." Draw ray diagram to justify this statement stating the position of the object with respect to the lens in each case. An object of height 4 cm is placed at a distance of 20 cm from a concave lens of focal length 10 cm. Use lens formula to determine the position of the image formed. 24) A student is unable to see clearly the words written on the blackboard placed at a distance of approximately 4 m from him. Name the defect of vision the boy is suffering from. Explain the method of correcting this defect. Draw ray diagram for the: (i) defect of vision and also (ii) for its correction. SECTION-B 25) A student adds 2 ml of acetic acid to a test tube containing 2 ml of distilled water. He then shakes the test tube well and leaves it to settle for some time. After about 5 minutes he observes that in the test tube there is: (A) a clear transparent colourless solution (B) a clear transparent pink solution (C) a precipitate settling at the bottom of the test tube (D) a layer of water the layer of acetic acid

75 26) A student Prepared 20% sodium hydroxide solution in a beaker to study saponification reaction. Some observations related to this are given below: (I) Sodium hydroxide solution turns red litmus blue (II) Sodium hydroxide readily dissolves in water (III) The beaker containing solution appears cold when touched from outside (IV) The blue litmus paper turns red when dipped into the solution The correct observations are : (A) I, II and IV (B) I, II and III (C) only III and IV (D) only I and II 27) Hard water is not available for an experiment. Some salts are given below : (I) Sodium chloride (II) Sodium sulphate (III) Calcium chloride (IV) Calcium sulphate (V) Potassium chloride (VI) Magnesium sulphate Select from the following group of these salts, each member of which may be dissolved in water to make it hard. (A) I, II, V (B) I, III, V (C) III, IV, VI (D) II, IV, VI 28) A student identified the various parts of an embryo of a gram seed and listed them as given below : (I) Testa (II) Plumule (III) Radicle (IV) Cotyledon (V) Tegmen Out of these the actual parts of the embryo are : (A) I, II, III (B) II, III, IV

76 (C) III, IV, V (D) II, IV, V 29) Four students A, B, C and D reported the following set of organs to be homologous. Who is correct? (A) Wings of a bat and a butterfly (B) Wings of a pigeon and a bat (C) Wings of a pigeon and a butterfly (D) Forelimbs of cow, a duck and a lizard 30) Study the following diagram and select the correct statement about the device 'X' : (A) Device 'X' is a concave mirror of radius of curvature 12 cm (B) Device 'X' is a concave mirror of focal length 6 cm (C) Device 'X' is a concave mirror of focal length 12 cm (D) Device 'X' is a convex of mirror of focal length 12 cm 31) A student has obtained a point image of a distant object using the given convex lens. To find the focal length of the lens he should measure the distance between the : (A) lens and the object only (B) lens and the screen only (C) object and the image only (D) lens and the object and also between the object and the image 32) For students P, Q, R and S traced the path of a ray of light passing through a glass slab for an angle of incidence 40 and measured the angle of refraction. The values as measured them were 18 ; 22 ; 25

77 and 30 respectively. The student who has performed the experiment methodically is (A) P (B) Q (C) R (D) S 33) After tracing the path of a ray of light through a glass prism a student marked the angle of incidence ( i), angle of refraction ( r) angle of emergence ( e) and the angle of deviation ( D) as shown in the diagram. The correctly marked angles are: (A) i and r (B) i and e (C) i, e and D (D) i, r and e 34) List two observations which you make when you add a pinch of sodium hydrogen carbonate to acetic acid in a test tube. Write chemical equation for the reaction that occurs. 35) Name the types of asexual reproduction in which two individuals are formed from a single parent and the parental identity is lost. Draw the initial and the final stages of this type of reproduction. State the event with which this reproduction starts. 36) To find the image-distance for varying object-distances in case of a convex lens, a student obtains on a screen a sharp image of a bright object placed very far from the lens. After that he gradually moves the object towards the lens and each time focuses its image of the screen. (a) In which direction towards or away from the lens, does he move the screen to focus the object? (b) What happens to the size of image does it increase or decrease? (c) What happen when he moves the object very close to the lens?

78 CBSE-CLASS-X-SCIENCE -SOLUTIONS-2015 SECTION-A 1) C n H 2n is the general formula for the alkene series. The second member of the alkene family is propene with the molecular formula C 3 H 6. 2) Two functions performed by the testis in human beings are as follows: 1. It secretes the hormone testosterone, which is responsible for the secondary sexual changes in males. 2. It produces sperms, which participate in fertilisation. 3) The function of the ozone (O 3 ) layer in the upper atmosphere is to prevent harmful ultraviolet (UV) rays from reaching the Earth's surface, as these UV rays cause various types of diseases including skin cancer. 4) Four characteristics of the images formed by plane mirrors are as follows: 1. The images are of the same size as that of the objects 2. The images are formed behind the mirrors at the same distance from the mirrors as that of the objects. 3. The images formed are virtual and erect. 4. The images are laterally inverted. 5) Forests are considered "biodiversity hot spots" because they contain a high level of species diversity threatened with extinction. The following are the two ways in which a person can effectively contribute towards the management of forests and wildlife: 1. He/she can avoid throwing non-biodegradable wastes, such as plastic bottles, in forest-protected areas. 2. He/she can reduce the use of products directly derived from forests (such as wood) and animals (such as animal skin). 6) Sustainable Management It is a pattern of management that promises the use of natural resources in such a way that they meet the human needs not only in the present but also in the future. Advantage of Reuse over Recycling Reusing a material is better that recycling it because recycling requires a large amount of energy and money. Reuse, on the other hand, preserves the embodied energy originally used in manufacturing an item. Reuse also creates less air and water pollution than recycling.

79 7) The process of adding hydrogen to an unsaturated compound is called hydrogenation. For example, the hydrogenation of ethene leads to the formation of ethane. Conditions for Hydrogenation (i) Presence of an unsaturated compound (i.e. an unsaturated hydrocarbon) (ii) Presence of a catalyst such as finely divided palladium or nickel In case of the hydrogenation of vegetable oils, liquid unsaturated fatty acids are converted into solid saturated fatty acids. 8) Soap molecules are sodium or potassium salts of long-chain carboxylic acids. They form scum upon reaction with calcium and magnesium ions present in hard water. Detergent molecules are ammonium or sulphonate salts of long-chain carboxylic acids. They do not form insoluble precipitates with calcium and magnesium ions. Cleansing action of soaps: The dirt present on clothes is organic in nature and is insoluble in water. Therefore, it cannot be removed by only washing with water. When soap is dissolved in water, its hydrophobic ends attach themselves to the dirt and remove it from the cloth. Then, the molecules of soap arrange themselves in micelle formation and trap the dirt at the centre of the cluster. These micelles remain suspended in the water and thus, the dust particles are easily rinsed away by water.

80 9) There are 18 groups and 7 periods in the modern periodic table. (a) The atomic size and metallic character of elements increases down a group. (b) The atomic size and metallic character of elements decreases from left to right in a period. 10) (i) Among the given elements, 19 K has one electron in the outermost shell. Its electronic configuration is 2, 8, 8, 1. (ii) The elements 4 Be and 20 Ca belong to the same group, that is, Group 2. They both have two electrons each in their outermost shells. Electronic configuration of 4Be is 2, 2. Electronic configuration of 20 Ca is 2, 8, 8, 2. Atomic number of element X = 17 Electronic configuration of element X is 2, 8, 7. Number of valence electrons in X = 7 Valency of X = 8 7 = 1 Atomic number of K = 19 Electronic configuration of K is 2, 8, 8, 1 Number of valence electrons in K = 1 Valency of K = 1

81 Therefore, the formula of the compound formed when K and element X combine is KX. The compound KX is of ionic nature. 11) DNA Copying It is the process of production of a new DNA molecule from an already existing DNA molecule through chemical reactions. It is accompanied with the creation of new cellular apparatus so that the daughter DNA and parent DNA can be separated. Importance of DNA copying 1. It helps in the transmission of characteristics from parents to offspring. 2. It helps in the formation of a new cell from the parent cell. 12) Budding It involves the formation of a new individual from a protrusion called bud. It is very common in plants, yeasts and lower-level animals such as Hydra. In Hydra, the cells divide rapidly at a specific site and develop as an outgrowth called bud. These buds, while attached to the parent body, develop into small individuals. When this individual becomes large enough, it detaches itself from the parent body to exist as an independent individual. 13) Four methods of contraception that can be used by humans are as follows: (i) Natural method: In this method, the sexual act is avoided from the 10th day to the 17th day of the menstrual cycle, as ovulation is expected during this period and the chances of fertilisation are very high. (ii) Barrier method: In this method, the fertilisation of the ovum and the sperm is prevented with the help of a barrier such as a condom. (iii) Oral contraceptive method: In this method, tablets or drugs are taken orally to prevent fertilisation. (iv) Implants and surgical methods: Contraceptive devices, such as a loop and a Copper-T rod, are placed in the uterus to prevent pregnancy. However, they can cause side effects to the uterus. Some surgical methods such as vasectomy (blocking of the vas deferens in the male body to prevent the transfer of sperms) and tubectomy (blocking of fallopian tubes in the female body to prevent the egg

82 from reaching the uterus) can also be used to block the gamete transfer. The following are the effects of contraception on the health and prosperity of a family: (i) It helps in preventing unwanted pregnancies. (ii) It prevents the chances of frequent pregnancies, which, otherwise, affect the health of females. (iii) It helps in family planning by controlling the number of children in a family. (iv) It also reduces the chances of transmission of sexually transmitted diseases such as AIDS. In this way, birth control methods play an important role in the health and prosperity of a family. 14) The experiences and qualifications that a person earns during his/her lifetime are examples of acquired traits. These traits cannot be inherited. For example, a wrestler develops large muscles because of his training programme; it does not mean that his offspring will necessarily have large muscles. These characters do not affect the DNA make-up of germ cells of an organism; thus, they are not passed on to the next generation. On the other hand, inherited traits are the traits that are transferred from the parents to their offspring. Inherited traits are coded by genes present in the DNA of gamete cells from where they are transferred to the progeny. Examples of inherited traits are skin colour and eye colour. 15) (i) The eyes seen in Planaria, insects, octopus and vertebrates vary greatly in their structure. These organisms can be used for studying the evolution of eyes as the eye of Planaria is simple without lens, insects have compound eyes and vertebrates have highly specialised eyes; however, all of them perform same function, that is, vision. Thus, a common evolutionary origin can be established on the basis of eyes. (ii) Birds have evolved from reptiles as the connecting link between reptiles and birds is Archaeopteryx (flying dinosaur). Also, there are some similarities in birds and reptiles. Birds have four-chambered heart, which is also a feature of some reptiles; both birds and reptiles are oviparous and have separate sexes and internal fertilisation occurs in both birds and reptiles. 16) The two rays chosen to construct a ray diagram are shown in the ray diagram given below:

83 (i) Ray I: When the incident ray is parallel to the principal axis, the reflected ray will pass through the focus of concave mirror or it appears to pass through the focus of convex mirror. (ii) Ray II: When the incident ray passes through or appears to pass through the centre of curvature, the light, after reflection from the spherical mirror, reflects back along the same path. The image formed is real, inverted and magnified. It is formed beyond the centre of curvature. 17) At sunrise and sunset, the Sun is near the horizon and its rays cover a larger part of the atmosphere. As the intensity of the scattered light is inversely proportional to the wavelength of the color, therefore, most of the blue light and other components of shorter wavelength are scattered away by the particles. The wavelength of the red color is the longest among all the components of white light; therefore, it is

84 least scattered and appears to come from the sun. Hence, the Sun looks red at the time of sunrise and sunset. 18) (a) Burning plastic is not an eco-friendly method of waste disposal because it causes air pollution by producing harmful gases. Rakesh's method of waste disposal is advantageous as the leftover food and peels of fruits are biodegradable material and can serve as manure, whereas plastic bags and cans should be disposed off in blue dustbins as they are non-biodegradable and can be recycled manually; thus, keeping the environment clean. (b) We can keep the parks and roads clean by throwing the biodegradable waste in green dustbins and the non-biodegradable waste in blue dustbins stopping people from spitting on roads and parks. 19) Carbon has 4 electrons in its outermost shell and requires 4 more electrons to attain a noble gas electronic configuration. It cannot form a C 4+ ion, as the removal of 4 valence electrons requires a huge amount of energy. The C 4+ ion thus formed will have 6 protons and 2 electrons, which will make it highly unstable. Carbon cannot form a C 4 ion, as its nucleus with 6 protons cannot hold 10 electrons due to inter electronic repulsion. So, carbon achieves a noble gas electronic configuration only by sharing its 4 valence electrons with other elements. Thus, it forms compounds mainly by covalent bonds. The two main reasons for carbon forming a large number of compounds are as follows: (a) Catenation: It is the ability of carbon to form bonds with other carbon atoms; this results in compounds having long branched chains and rings. (b) Tetravalency: Carbon has 4 valence electrons, so it is capable of forming covalent bonds with 4 other atoms. Carbon forms strong bonds with most other elements. This is because the small atomic size of carbon enables its nucleus to strongly hold on to the shared pairs of electrons. 20)

85 Functions of the Ovary It produces female gametes (ova). It secretes female sex hormones. It secretes inhibin involved in the feedback control of pituitary FSH production. Functions of the Oviduct Fertilisation takes place here. The fertilised ovum travels towards the uterus through the fallopian tube. Functions of the Uterus It supports and nourishes the developing foetus. It expands according to the growth of the baby. The embryo develops inside the mother s body for about nine months. Inside the uterus, the outer tissue surrounding the embryo develops finger-like projections called villi. These villi are surrounded by uterine tissue and maternal blood. They provide a large surface area for the exchange of oxygen and nutrients. There is a special tissue called placenta embedded in the uterine wall. The embryo receives the oxygen and nutrients from the mother s blood via the placenta. The waste material produced by the embryo is removed through the placenta. 21) Twenty-three pairs of chromosomes are present in human beings. Out of these, one pair is of sex chromosomes. Two types of sex chromosomes are found in human beings: X and Y. Males contain one X chromosome and one Y chromosome (XY), while females contain two copies of X chromosomes (XX). The sperm has either X or Y chromosome, while the egg has only X chromosome. So, if the sperm carrying Y chromosome fuses with the egg, it results in the formation of a male child; and if the sperm carrying X chromosome fuses with the egg, it results in the formation of a female child. Thus, there is an equal chance of fusion of either X or Y chromosome with the egg. Therefore, we can say that the sex of a newborn child is a matter of chance and none of the parents are responsible for it. Sex determination in humans is shown below:

86 22) (a) Laws of Refraction: (1) The incident ray, the refracted ray and the normal to the interface of two media at the point of incidence all lie in the same plane. (2) For the light of a given color and for given pair of media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant. This is also known as Snell's Law. Mathematically, it can be given as follows: sin i = constant = A sin r µ B Here, A µ is the relative refractive index of medium B with respect to medium A. B The absolute refractive index is the value of refractive index of a medium with respect to the vacuum. c µ B = υ Where c = Speed of light in vacuum v = Speed of light in medium B Here, µ is the absolute refractive index of medium B. B (b) Absolute refractive index of medium 'A', µ = 2. 0 A Absolute refractive index of medium 'B', 0 (i) For medium 'B', µ B = 2.

87 c 1.5 = 8 (2 10 ) 8 c = c = 3 10 Speed of light in vacuum is 8 c = 3 10 ms -1 (ii) For medium 'A', c µ A = υ c υ = µ A υ = 2 8 υ = Thus, speed of light in medium 'A' is ms ) (a) Magnified erect image (When the object is placed between O and F 1 ) (b) Magnified inverted image (When the object is placed between F 1 and 2F 1 )

88 Object distance, u = 20 cm Image distance, v =? Focal length, f = 10 cm As per the sign conventions used, f = 10 cm u = 20 cm According to the lens formula, = f υ u = + υ f u = + = υ υ = = 6.6 cm 20 The image is formed at a distance of 6.6 cm from the lens at the same side where the object is placed. 24) As the student is not able to clearly see the words written on the blackboard that is at a distance of approximately 4 m from him, the student is suffering from the defect called myopia or near-sightedness. A myopic eye has its far point nearer than infinity. It forms the image of a distant object in front of its retina. To correct a myopic eye, concave lens of a suitable focal length is used. The image is allowed to form at the retina by using a concave lens of suitable power. (i) A myopic eye (ii) Correction of myopia using concave lens (a) Far Point of Myopic Eye

89 (b) Distant Vision of Myopic Eye Correction of Myopic Eye SECTION-B 25) Acetic acid dissolves completely in distilled water and gives a clear, colourless and transparent solution. Hence, the correct option is A. 26) Sodium hydroxide is a base. It readily dissolves in water to form an alkaline solution, which turns red litmus paper blue. When sodium hydroxide is dissolved in water, a large amount of heat is evolved, as the process is exothermic in nature. Thus, the beaker containing the sodium hydroxide solution should feel hot when touched from the outside. Hence, the correct option is D. 27) Hard water contains sulphates, chlorides and bicarbonates of calcium and magnesium. To make water hard, calcium chloride, calcium sulphate and magnesium sulphate should be added to it. Hence, the correct option is C. 28) Plumule, radicle and cotyledon are the actual parts of the embryo of a gram seed. Testa and tegmen are the parts of the seed coat. Hence, the correct option is B. 29) Homologous organs are the organs that have a similar origin and basic structure but different functions. Forelimbs of a cow, a duck and a lizard have a similar structure but different functions. Hence, the correct option is D. 30) Because the light rays coming from infinity get reflected by the device 'X' and converge at a point at a distance 12 cm from it, the device 'X' is a concave mirror of focal length 12 cm. Hence, the correct option is C.

90 31) In the given case, the student has obtained the point image of a distant object using a convex lens. According to the lens formula, = f υ u Here, v = Image distance u = Object distance f = Focal length of the lens Because the object is placed very far, the object distance is taken to be infinity. As u = 1 Thus, = 0 and f = v. u To find the focal length of the lens, the student should know the image distance, which is the distance between the lens and the screen. Hence, the correct option is B. 32) The student R has performed the experiment methodically. The reason can be explained using Snell's law. According to Snell's law, sin i sin r = µ g Here, i = Angle of incidence r = Angle of refraction μ g = Refractive index for glass The angle of refraction measured by student R is most appropriate as it verifies the Snell's law. Given: i = 40 o The angle of refraction measured by student R, r = 25 o. Also, sin40 o = sin25 o = Now, sin = = 1.52 sin The refractive index for glass is 1.5; it verifies the result derived above. Hence, the correct option is C.

91 Disclaimer: The values of sin40 o and sin25 o can be obtained using trigonometric tables. 33) In the given diagram, the angle of incidence ( i) and the angle of emergence ( e) have been correctly marked. Hence, the correct option is B. Disclaimer: In the question paper the angle of emergence e is drawn incorrectly as it is shown between the normal and the surface of the prism. 34) When a pinch of sodium hydrogen carbonate is added to acetic acid in a test tube, a brisk effervescence is observed due to colourless and odourless gas, which is CO 2. Chemical equation for the reaction: CH 3 COOH(aq) + NaHCO 3 (s) CH 3 COONa(aq) + H 2 O(l) + CO 2 (g) 35) Binary fission is the type of asexual reproduction in which two individuals are formed from a single parent and the parental identity is lost. Initial and Final Stages of Binary Fission This reproduction starts with karyokinesis (division of nucleus). 36) (a) As the student moves the object towards the lens, the position of the image shifts away from the lens. To obtain a sharp image, he should move the screen away from the lens. (b) The size of the image increases when the object is moved near the lens. (c) When the object is placed very close to the lens, it can be considered to be placed between the focus and the optical centre. In this case, the image formed is virtual, erect and enlarged.

92 CBSE Class-X-SCIENCE-2011 General Instructions: (i) (ii) (iii) (iv) (v) (vi) (vii) (viii) (ix) The question paper comprises of two sections A and B. You are to attempt both the sections. All questions are compulsory. There is no overall choice. However internal choice has been provided in all the three question of five marks category. Only one option in such question is to be attempt. All questions of section A and all questions of section B are to be attempted separately. Questions numbers 1 to 4 in section A are one mark questions. These are to be answered in one word or one sentence. Question numbers 5 to 13 are two mark questions, to be answered in about 30 words each. Question numbers 14 to 22 are three mark questions to be answered in about 50 words each. Question numbers 23 to 25 are five mark questions, to be answered in about 70 word each. Question numbers 26 to 41 in section B are multiple choice questions based on practical skills. Each question is a one mark question. You are to select one most appropriate response out of the four provided to you. Q1. What are the various steps in a food chain called? Q2. What is the important function of presence of ozone in earth s atmosphere? Q3. Write the electron dot structure of ethane molecule, C 2 H 6. Q4. What makes the earth s atmosphere a heterogeneous mixture? Q5. List any four characteristics of a good fuel. Q6. What are non-renewable resources of energy? Give two examples of such resources.

93 Q7. (i) How do you calculate the possible valency of an element from the electronic configuration of its atoms? (ii) Calculate the valency of element X whose atomic number is 9. Q8. On the basis of electronic configuration, how will you identify the first and the last element of a period? Q9. State the two laws of reflection of light. Q10. The stars appear higher from horizon than they actually are. Explain why it is so. Q11. Explain why the planets do not twinkle but the stars twinkle. Q12. Write any two differences between binary fission and multiple fission in a tabular form as observed in cells of organisms. Q13. Why is DNA copying an essential part of the process of reproduction? Q14. Explain the terms: (i) Speciation (ii) Natural selection Q15. Explain how equal genetic contribution of male and female parents is ensured in the progeny. Q16. Out of HCI and CH 3 COOH, which one is a weak acid and why? Describe an activity to support your answer. Q17. Two elements X and Y belong to group 1 and 2 respectively in the same period of periodic table. Compare them with respect to: (i) The number of valence electrons in their atoms (ii) Their valencies (iii) Metallic character (iv) The sizes of their atoms (v) The formulae of their oxides (vi) The formulae of their chlorides

94 Q18. Draw the ray diagram and also state the position, the relative size and the nature of image formed by a concave mirror when the object is placed at the centre of curvature of the mirror. Q19. (i) The refractive index of diamond is What is the meaning of this statement? (iii) Name a liquid whose mass density is less than that of water but it is optically denser than water. Q20. What eye defect is hypermetropia? Describe with a ray diagram how this defect of vision can be corrected by using an appropriate lens. Q21. (a) List two sexually transmitted disease in each of the following cases: (i) Bacterial infections (ii) Viral infections (b) How may the spread of such diseases be prevented? Q22. Explain Mendel s law of independent inheritance. Give one example. Q23. (a) If the image formed by a lens is diminished in size and erect, for all positions of the object, what type of lens is it? (b) Name the point on the lens through which a ray of light passes undeviated. (c) An object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 30 cm. Find (i) the position (ii) the magnification and (iii) the nature of the image formed. OR (a) One half of a convex lens is covered with a black paper. Will such a lens produce an image of the complete object? Support your answer with a ray diagram. (b) An object 5 cm high is held 25 cm away from a converging lens of focal length 10 cm. (i) Draw the ray diagram and (ii) Calculate the position and size of the image formed.

95 (iii) What is the nature of the image? stigma. Q24. (a) Draw a diagram of the longitudinal section of a flower and label on it sepal, petal, ovary and (b)write the names of male and female reproductive parts of a flower. OR (a) What is fragmentation in organisms? Name a multicellular organism which reproduces by this method. (b) What is regeneration in organism? Describe regeneration in Planaria with the help of a suitable diagram. Q25. (a) In a tabular form, differentiate between ethanol and ethanoic acid under the following heads: (i) Physical state (ii) Taste (iii) NaHCO 3 test (iv) Ester test (b)write a chemical reaction to show the dehydration of ethanol. OR (a) What is soap? Why are soaps not suitable for washing clothes when the water is hard? (b) Explain the action of soap in removing an oily spot from a piece of cloth. Q26. A Student was given two permanent slides, one of binary fission in amoeba and other of budding in yeast. He was asked to identify any one difference in the nucleus of the two. One such difference, he identified correctly was (1) Presence of one nucleus in amoeba, two in yeast cell and one in bud. (2) Presence of two nuclei in centrally constricted amoeba, one in yeast cell and one in its bud. (3) Presence of two distant nuclei in amoeba, one in yeast cell and two in bud. (4) Presence of a single nucleus each in amoeba, yeast cell and its attached bud. Q27. Binary fission is observed in which one of the following figures?

96 Q28. To determine the percentage of water absorbed by raisins, raisins are soaked in water for: (1) 30 Seconds (2) 10 minutes (3) 2 to 3 hours (4) 24 hours Q29. Raisins are wiped off gently before final weighing with help of (1) A filter paper (2) A cotton piece (3) A cloth piece (4) A polythene piece Q30. The step (S) necessary for determing the percentage of water absorbed by raisins is/are: (1) Raisins should be completely immersed in water (2) Raisins should be soaked in water for sufficient time (3) Gently wipe dry the soaked raisins (4) All of the above steps.

97 Q31. Rahim recorded the following sets of observations while tracing the path of a ray of light passing through a rectangular glass slab for different angles of incidence. The correct observation is recorded at serial number: (1) I (2) II (3) III (4) IV (32) Four students A, B, C and D traced the paths of incident ray and the emergent ray by fixing pins P and Q for incident ray and pins R and S for emergent ray for a ray of light passing through a glass slab. The correct emergent ray was traced by the student:

98 (1) A (2) B (3) C (4) D Q33. Mohan obtained a sharp inverted image of a distant tree on the screen behind the lens. He then moved the screen and tried to look through lens in the direction of the object. He would see: (1) A blurred image on the wall of the laboratory. (2) An erect image of the tree on the lens. (3) No image as the screen has been removed. (4) An inverted image of the tree at the focus of the lens. Q34. For finding the focal length of a convex lens by obtaining the image of a distant object, one should use as the object. (1) A well lit distant tree. (2) Window grill in the class room. (3) Any distant tree. (4) A lighted candle kept at the other end of the table. Q35. To find the focal length of a concave mirror Rahul focuses a distant object with his mirror. The chosen object should be (1) A tree (2) A building (3) A window (4) The sun Q36. The colour of an aqueous solution of Zinc sulphate as observed in the laboratory is: (1) Green (2) Yellow (3) Blue (4) Colourless Q37. To show that zinc is a more active metal than copper, the correct procedure is to: (1) Add dilute nitric acid on strips of both the metals.

99 (2) Observe transmission of heat through strips of zinc and copper. (3) Prepare solution of zinc sulphate and hang strip of copper into it. (4) Prepare solution of copper sulphate and hang strip of zinc into it. Q38. Acetic acid smells like: (1) A banana (2) Vinegar (3) An orange (4) A lemon Q39. Acetic acid solution turns: (1) Blue litmus red (2) Red litmus blue (3) Blue litmus colourless (4) Red litmus colourless Q.40. on adding NaHCO 3 to acetic acid, a gas is evolved which turns lime water milky due to the formation of: (1) Calcium bicarbonate (2) Calcium hydroxide (3) Calcium carbonate (4) Calcium acetate Q41. An Yeast cell in which budding occurs was seen to have: (1) One bud cell (2) Two bud cell (3) Three bud cell (4) A chain of bud cells

100

101 For more previous year question papers visit :

102

103

104

105

106

107

108

109

110

111

112

113

114

115 For more previous year question papers visit :

116

117

118

119

120

121

122

123

124 CBSE CLASS X-Science-Solution 1. Solution: The various steps in a food chain are called trophic levels. 2. Solution: The ozone layer prevents the harmful UV rays from entering into the earth s atmosphere. 3. Solution: The electron dot structure of ethane molecule, C 2 H Solution: The earth s atmosphere is heterogeneous as it typically consists of 21% oxygen, 78% nitrogen, 0.93% argon and 0.03% CO 2 with other gases making up the remaining percentage. 5. Solution: I. It should possess low Ignition temperature. II. It should not leave residue after burning, i.e., it should burn completely. III. It should burn without producing too many pollutants. IV. It should be easily available and accessible V. It should be economical. VI. It should be easy to store and transport. (Any four of the above six will solve the purpose).

125 6. Solution: Non renewable resources of energy are those energy resources that are consumed at a rate faster than the rate at which they are replenished. Two examples of non-renewable resources are coal and petroleum. 7. Solution: (i) Number of valence electrons 4: valency = number of valence electrons Number of valence electrons > 4: valency = 8 number of valence electrons. (ii) The electronic configuration of element x with atomic number 9 is 2,7. Its valency = 8 7 = 1 Hence, the valency of element with atomic number 9 is Solution: If the number of valence electron is 1 then the element is said to be the first element of a period, if the number of valence electrons are 8, the element is said to be the last element of a period. 9. Solution: The two laws of reflection can be stated as follows: i. The angle of incidence is equal to the angle of reflection. ii. The incident ray, the reflected ray and the normal to the mirror, all lie in the same plane. 10. Solution: Stars appear slightly higher from the horizon due to atmospheric refraction. The atmosphere bends the starlight towards the normal. This apparent positioning is not stationary but keeps changing. 11. Solution: The planets being closer to the Earth do not appear as point sources of light. The planet covers a small circular area in space, when viewed from Earth. So, even if light from one point in the circular disc is blocked, light from other points reaches our eyes. As the light from the planets are not completely blocked from our sight and they do not twinkle. Stars on the other hand are point sized objects and twinkle by atmospheric refraction of light. 12. Solution: Two differences between binary fission and multiple fission are as follows: Binary Fission In binary fission, the single cell divides into halves. Binary fission is of two types; along any plane or longitudinally. Example: Amoeba (along any plane), Leishmania (longitudinally) Multiple fission In multiple fission, a single cell divides into many daughter cells simultaneously. Multiple fission occurs along only one plane Example: Plasmodium 13. Solution: DNA copying is an important process that ensures that when cell multiplies, through the mechanisms of mitosis or meiosis, the equal amount of DNA (genetic material) passes in to the new cell. The DNA replicates so that there will be an extra copy of DNA when the cell multiplies.

126 14. Solution: (i) Speciation Speciation is an evolutionary phenomenon by which new species are formed. There are three models of speciation: (1) When the groups that evolve to be separate species are in different geographic locations and are isolated geographically from each other. (2) When the groups that evolve to be separate species are geographic near and the individuals can move one species area to others. (3) When the groups that evolve to be separate species occur together in the same geographic area. (iii) Natural selection Natural selection is a key mechanism in evolution. It is a process that results in an increased survival and reproductive success of individuals that are well adjusted to the environment. The theory of natural selection was given by Charles Darwin. 15. Solution. The genetic material of a cell is stored in the DNA. During sexual reproduction, the genetic material from both the parents is transferred to the offspring. All human beings have 23 pairs of chromosomes out of which two chromosomes are sex chromosomes. These sex chromosomes are responsible for determining the sex of a child. (i) (ii) (iii) The sex chromosomes are represented by X and Y. Females have two X chromosomes (XX) and males have one X and one Y chromosome (XY). The gametes receive half of the chromosomes so the male gametes would be 22 + X or 22 + Y and since females have X chromosomes their have 22 + X chromosomes. So the sex of the baby is determined by the type of male gamete which fuses with the female. 16. Solution:

127 CH 3 COOH is a weak acid when compared to HCI because HCI completely dissociates into ions in solution whereas CH 3 COOH being weak acid is partially dissociated into ions in solution. This can be proved by the following activity: Two iron nails are fitted on a cork and are kept in a 100 ml beaker. The nails are then connected to the two terminals of a 6 volt battery through a bulb and a switch. Some dilute HCI is poured in the beaker and the current is switched on. The same experiment is then performed with CH 3 COOH. Observations: It will be observed that the bulb glows in the HCI solution and does not glow in the CH 3 COOH solution. Inference: HCI, being a strong acid dissociates into H + and CI - ions. These ions conduct electricity in the solution resulting in the glowing of the bulb. On the other hand, the CH 3 COOH is a weak acid. It does not dissociate into ions completely in solution. Therefore, it does not conduct electricity. 17. Solution: (i) The number of valence electrons in element X is 1 while in element Y is 2. (ii) The valency of element X is 1 and that of element Y is 2. (iii) Element X is more metallic than element Y. (iv) The size of atom X is more than that of atom Y. (v) The formula of oxide of element X is X 2 O and that of element Y is YO. (vi) The formula of chloride of element X is XCI and that of element Y YCI Solution:

128 Position of the image: at the centre of curvature Size of the image: Enlarged Nature of the image: Real and inverted 19. Solution: (i) (ii) The refractive index of diamond is This means the ratio of sine of angle of incidence to the sine of angle of refraction is equal to Kerosene has refractive index of 1.44, its mass density is less than that of water but it is optically denser than water (kerosene: 1.44 and water: 1.33). 20. Solution: Hypermetropia is a defect of vision in which a person cannot see nearby objects clearly, but has no problems in seeing distant objects. Corrected vision for a hypermetropic eye by using a convex lens: 21. Solution: (a) Two sexually transmitted disease in each of the following cases are: (i) Bacterial infections: syphilis, Gonorrhoea (ii) Viral infections: AIDS, Genital Herpes

129 (b) The spread of sexually transmitted diseases can be prevented by using condoms and avoiding multiple partners. 22. Solution: Mendel s law of independent assortment states that When two pairs of traits are combined in a hybrid, one pair of character segregates independent of the other pair of character. In a dihybrid cross between two plants having round yellow (RRYY) and wrinkled green seeds (rryy), four types of gametes (RY, Ry, ry, ry) are produced. Each of these segregate independent of each other, each having a frequency of 25% of the total gametes produced. 23. Solution: (a) If the image formed by a lens is diminished in size and erect, for all positions of the object, then the lens is a concave lens. (b) The point on the lens through which a ray of light passes undeviated is known as Pole. (c) 1 = = uu ff v= ; f = 20cm, u= 30cm ff vv uu vv ff uu uu+ff

130 ( 30) 20 (i) V = = 60cm The image is formed at a distance of 60 cm on the other side of the optical centre (ii) m = vv = 60 uu 30 (iii) Image formed is inverted. OR (a) The image is formed by a large number of rays from the object. So, even if one half of the lens is darkened, the image will form. However, the brightness of the image will be less as compared to that of the image formed without wrapping the lens. 1 (i) = = ff vv uu vv ff uu (ii) ( 25) 10 v= = 16.67cm (iii) m = vv uu = h ii h oo ( 25) uu ff v= ; f = 10cm, u= 25cm uu+ff vv h h i = oo = = 3.34cm uu Negative sign indicates that the image is real and inverted.

131 24. Solution: (a) (b) The male reproductive part of flower is called stamen that consists of filaments and anthers. The female reproductive part of the flower is pistil that consists of stigma, style and ovary. OR (a) Fragmentation is a made of asexual reproduction. It is the unintentional cutting up of the body of an organism. Each fragment develops into a new individual. Example: Spirogyra (b) Regeneration: Regeneration involves the capacity of an organism to give rise to an entire individual from a portion. This type of regeneration occurs in Planaria. When Planaria gets cut unintentionally, the cut fragments give rise to a new individual. In this type, active cell division occurs before the replacement. The newly formed mass undergoes differentiation to form specialized cells.

132 25. Solution: (a) (i)physical state Eathanol is a colourless liquid with Pleasant odour Ethanoic acid is colourless, pungent smelling liquid (ii) Taste Ethanol is bitter to taste Ethanoic acid is sour to taste (iii) NaHCO 3 Ethanol does not react with sodium Bicarbonate When ethanoic acid reacts with sodium NaHCO 3 with the evolution of carbon dioxide gas. (iv)ester test Ethanol on reaction with ethanoic acid in the presence of acid forms ester (b) Ethanol undergoes dehydration to form ethane. Ethanoic acid on reaction with ethanol in the presence 2CH 3 CH 2 OH 2 CH 2 = CH 2 + 2H 2 O Ethanol Ethene OR (a) A soap can be defined as a sodium or potassium salt of higher fatty acids such as oleic acid (C 17 H 33 COOH), stearic acid (C 17 H 35 COOH), palmitic acid (C 15 H 31 COOH), etc. Soap does not work properly when the water is hard. A soap is a sodium or potassium salt of long chain fatty acids. Hard water contains salts of calcium and magnesium. When soap is added to hard water, calcium and magnesium ions present in water displace sodium or potassium ions

133 from the soap molecules forming an insoluble substance called scum. A lot of soap is wasted in the process. (b) Cleaning action of soaps: The oily spot present on clothes is organic in nature and insoluble in water. Therefore, it cannot be removed by only washing with water. When soap is dissolved in water, its hydrophobic ends attach themselves to the oily spot and remove it from the cloth. Then, the molecules of soap arrange themselves in the form of micelle and trap the dirt at the centre of the cluster. These micelles remain suspended in the water. Hence, the oily spots are easily rinsed away by water. 26. Solution: (2) Presence of two nuclei in centrally constricted amoeba, one in yeast cell and one in its bud. 27. Solution: (1) A (2) B (3) C (4) D 28. Solution: (3) 2 to 3 hours