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Board Paper of Class 10 2012 Science (SET 3) - Solutions

General Instructions:
(i) The question paper comprises of two sections A and B. You are to attempt both the sections.
(ii) All questions are compulsory.
(iii) There is no over all 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.
(iv) All questions of section A and all questions of section B are to be attempted separately.
(v) Questions numbers 1 to 4 in section A are one mark questions. These are to be answered in one word or one sentence.
(vi) Question numbers 5 to 13 are two mark questions, to be answered in about 30 words each.
(vii) Question numbers 14 to 22 are three mark questions to be answered in about 50 words each.
(viii) Question numbers 23 to 25 are five mark questions, to be answered in about 70 word each.
(ix) 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.


  • Question 1

    Name the functional group present in each of the following compounds:

    (i) CH3COCH3

    (ii) C2H5CHOOH

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  • Question 2

    Which phenomenon is responsible for making the path of light visible?

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  • Question 3

    Which class of carbon compounds is responsible for the depletion of ozone layer at the higher level of the atmosphere?

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  • Question 4

    Select two non-biodegradable substances from the following waste generated in a kitchen:

    Spoilt food, paper bags, milk bags, vegetable peels, tin cans, used tea leaves

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  • Question 5

    Define the term puberty. List two changes observed in girls at the time of puberty.

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  • Question 6

    What is meant by asexual reproduction? List its any two different forms.

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  • Question 7

    List four advantages of water stored in the ground.

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  • Question 8

    "Burning fossil fuels is a cause of global warming." Justify this statement.

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  • Question 9

    When we place a glass prism in the path of a narrow beam of white light a spectrum is obtained. What happens when a second identical prism is placed in an inverted position with respect to the first prism? Draw a labelled ray diagram to illustrate it.

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  • Question 10

    List four properties of the image formed by a convex mirror when object is placed between focus and pole of the mirror.

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  • Question 11

    An element 'M' has atomic number 12.

    (a) Write its electronic configuration.

    (b) State the group to which 'M' belongs.

    (c) Is 'M' a metal or a non-metal.

    (d) Write the formula of its chloride.

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  • Question 12

    How can the valency of an element be determined if its electronic configuration is known? What will be the valency of an element of atomic number 9 (nine)?

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  • Question 13

    A star sometimes appears brighter and some other times fainter. What is this effect called? State the reason for this effect.

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  • Question 14

    F, Cl and Br are the elements each having seven valence electrons. Which of these (i) has the largest atomic radius, (ii) is most reactive? Justify your answer stating reason for each.

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  • Question 15

    Explain the meaning of sexually transmitted diseases (STDs). Give two examples of STDs each, caused due to (i) bacterial infection and (ii) viral infection. State in brief how the spread of such diseases may be prevented.

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  • Question 16

    Distinguish between homologous organs and analogous organs. In which category would you place wings of a bird and wings of a bat? Justify your answer giving a suitable reason.

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  • Question 17

    Define the term ‘evolution’. “Evolution cannot be equated with progress”. Justify this statement.

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  • Question 18

    A blue colour flower plant denoted by BB is crossbred with that of white colour flower plant denoted by bb.

    (a) State the colour of flower you would expect in their F1 generation plants.

    (b) What must be the percentage of white flower plants in F2 generation if flowers of F1 plants are self-pollinated?

    (c) State the expected ratio of the genotypes BB and Bb in the F2 progeny.

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  • Question 19

    Complete the following equations:

    (a)

    (b)

    (c)

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  • Question 20

    A student cannot see a chart hanging on a wall placed at a distance of 3 m from him. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagrams for the (i) defect of vision and also (ii) for its correction.

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  • Question 21

    State the type of mirror preferred as (i) rear view mirror in vehicles, (ii) shaving mirror. Justify your answer giving two reasons in each case.

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  • Question 22

    The image of a candle flame placed at a distance 36 cm from a spherical lens is formed on a screen placed at a distance of 72 cm from the lens. Identify the type of lens and calculate its focal length. If the height of the flame is 2.5 cm, find the height of its image.

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  • Question 23

    List the sign conventions for reflection of light by spherical mirrors. Draw a diagram and apply these conventions in the determination of focal length of a spherical mirror which forms a three times magnified real image of an object placed 16 cm in front of it.

    OR

    State the law of refraction of light that defines the refractive index of a medium with respect to the other. Express it mathematically. How is refractive index of any medium 'A' with respect to a medium 'B' related to the speed of propagation of light in two media A and B? State the name of this constant when one medium is vacuum or air.

    The refractive indices of glass and water with respect to vacuum are 3/2 and 4/3 respectively. If the speed of light in glass is 2 × 108 m/s, find the speed of light in (i) vacuum, (ii) water.

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  • Question 24

    What is the difference between the chemical composition of soaps and detergents? State in brief the action of soaps in removing an oily spot from a shirt. Why are sops not considered suitable for washing where water is hard?

    OR

    List in tabular form three physical and two chemical properties on the basis of which ethanol and ethanoic acid can be differentiated.

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  • Question 25

    Define the terms pollination and fertilisation. Draw a diagram of a pistil showing pollen tube growth into the ovule and label the following:

    Pollen grain, male gamete, female gamete, ovary.

    OR

    Describe in brief the role of (i) testis (ii) seminal vesicle, (iii) vas deferens, (iv) ureter and (v) prostate gland in human male reproductive system.

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  • Question 26

    After observing the prepared slides of binary fission in Amoeba and budding in yeast following observations were reported:

    (a) Single cells of Amoeba and yeast were undergoing binary fission and budding respectively.

    (B) Cytokinesis was observed in the yeast cell.

    (C) Elongated nucleus was dividing to form two daughter nuclei in Amoeba.

    (D) A chain of buds were observed due to reproduction in Amoeba.

    The correct observation(s) is/are:

    (A) a and c

    (B) b only

    (C) c and d

    (D) d, a and c

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  • Question 27

    A student after viewing a prepared slide illustrates the budding in yeast in the following order which is not correct:

    (A) b, c, d, e, a

    (B) b, e, d, c, a

    (C) b, d, e, c, a

    (D) b, d, c, e, a

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  • Question 28

    A student has to observe a permanent slide of binary fission in Amoeba. Find the correct sequence of steps given below for focussing the object under a microscope.

    (a) Place the slide on the stage, look through the eye-piece and adjust the mirror to get proper illumination.

    (b) Focus the slide sharp using fine adjustment screw

    (c) Look through the eye-piece and raise the objective lens using coarse adjustment screw till the object is focussed.

    (d) Look through the eye-piece and move the slide till the object is visible.

    (A) d, c, b, a

    (B) a, b, d, c

    (C) a, d, c, b

    (D) a, c, d, b

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  • Question 29

    After viewing different slides, a student draws following diagrams. Select the one which depicts binary fission in Amoeba:

    (A) a

    (B) b

    (C) c

    (D) d

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  • Question 30

    Dry raisins were soaked in water for 2 hours, to determine the percentage of water absorbed by raisins. Before final weighing of swollen raisins, the extra water left on the surface of soaked raisins was removed by:

    (A) gently rubbing with cotton cloth

    (B) hot air blower

    (C) dry cotton wool

    (D) filter paper

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  • Question 31

    While performing the experiment with raisins to determine the percentage of water absorbed by them, a student made following measurements:

    Mass of water in the beaker = 40 g

    Mass of raisins before soaking = 5 g

    Mass of raisins after soaking for 2 hours = 8 g

    Mass of water left in the beaker after the experiment = 35 g

    The percentage of water absorbed by raisins is:

    (A)

    (B)

    (C)

    (D)

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  • Question 32

    Which of the following observations is true about dilute solution of acetic acid?

    (A) It smells like vinegar and turns red litmus blue

    (B) It smells like onion and turns blue litmus red

    (C) It smells like orange and turns red litmus blue

    (D) It smells like vinegar and turns blue litmus red

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  • Question 33

    A student takes Na2CO3 powder in a test tube and pours some drops of acetic acid over it. He observes:

    (A) no reaction in the test tube

    (B) colourless gas with pungent smell

    (C) bubbles of a colourless and odourless gas

    (D) white fumes with smell of vinegar

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  • Question 34

    A student adds 4 mL of acetic acid to a test tube containing 4 mL of distilled water. He then shakes the test tube and leaves it to settle. After about 10 minutes he observes:

    (A) a layer of water over the layer of acetic acid

    (B) a layer of acetic acid over the layer of water

    (C) a precipitate settling at the bottom of the test tube

    (D) a clear colourless solution

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  • Question 35

    The colours of aqueous solutions of CuSO4 and FeSO4 as observed in the laboratory are:

    (A) pale green and light blue respectively

    (B) light blue and dark green respectively

    (C) dark blue and dark green respectively

    (D) dark blue and pale green respectively

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  • Question 36

    A student prepared an aqueous solution of CuSO4 in beaker X and an aqueous solution of FeSO4 in beaker Y. He then dropped some iron pieces in beaker X and some zinc pieces in beaker Y. After about 10 hours he observed that the solutions in X and Y respectively appear:

    (A) blue and green

    (B) colourless and pale green

    (C) colourless and light blue

    (D) greenish and colourless

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  • Question 37

    While tracing the path of a ray of light passing through a rectangular glass slab a student tabulated his observations as given below:

    S.NO.

    ∠i

    ∠r

    ∠e

    I

    60°

    40°

    61°

    II

    50°

    36°

    51°

    III

    40°

    28°

    39°

    IV

    30°

    20°

    31°

    The correct observations is:

    (A) I

    (B) II

    (C) III

    (D) IV

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  • Question 38

    A student traces the path of a ray of white light through a rectangular glass slab and marks, the angles of incidence (∠i) , refraction (∠r) and emergence (∠e) as shown. Which angle or angles has he not marked correctly?

    (A) ∠i only

    (B) ∠i and ∠r

    (C) ∠i and ∠e

    (D) ∠r and ∠e

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  • Question 39

    To determine the focal length of a convex lens by obtaining a sharp image of a distant object we generally follow the following steps which are not in proper sequence.

    (a) Hold the lens between the object and the screen

    (B) Measure the distance between the lens and the screen

    (C) Select a well lit distant object

    (D) Place a screen opposite to the object on the lab table

    (e) Adjust the position of the lens to form a sharp image

    The correct sequence of these steps is:

    (A) c, a, d, e, b

    (B) c, d, a, e, b

    (C) c, d, e, a, b

    (D) c, a, e, d, b

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  • Question 40

    A student obtained a sharp image of the grills of a window on a screen using a concave mirror. His teacher remarked that for getting better results a well lit distant object (preferably the sun) should be focussed on the screen. What should be done for this purpose?

    (A) Move the screen slightly away from the mirror

    (B) Move the mirror slightly towards the screen

    (C) Move the screen and the mirror away from the object

    (D) Move the screen and the mirror towards the object

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  • Question 41

    To determine focal length of a concave mirror a student obtains the image of a well lit distant object on a screen. To determine the focal length of the given concave mirror he needs to measure the distance between:

    (A) mirror and the object

    (B) mirror and the screen

    (C) screen and the object

    (D) screen and the object and also mirror and the screen

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