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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

    Write the name and formula of the first member of the carbon compounds having functional group − CHO.


  • Question 2

    State one role of ciliary muscles in the human eye.


  • Question 3

    Write the name and formula of a molecule made up of three atoms of oxygen.


  • Question 4

    Name two decomposers operating in our ecosystem.


  • Question 5

    Why do all the elements of the (a) same group have similar properties, (b) same period have different properties?


  • Question 6

    An element E has following electronic configuration:







    (a) To which group of the periodic table does element E belong?

    (b) To which period of the periodic table does element E belong?

    (c) State the number of valence electrons present in element E.

    (d) State the valency of the element E.


  • Question 7

    Why is vegetative propagation practiced for growing some types of plant? List two plants which are grown by this method.


  • Question 8

    State the role of placenta in the development of embryo.


  • Question 9

    To construct ray diagram we use two light rays which are so chosen that it is easy to know their directions after reflection from the mirror. List these two rays and state the path of these rays after reflection. Use these rays to locate the image of an object placed between centre of curvature and focus of a concave mirror.


  • Question 10

    What is the colour of the clear sky during day time? Give reason for it.


  • Question 11

    Draw a labeled ray diagram to illustrate the dispersion of a narrow beam of white light when it passes through a glass prism.


  • Question 12

    List the products of combustion of fossil fuels. What are their adverse effects on the environment?


  • Question 13

    List three problems which arise due to construction of big dams. Suggest a solution for these problems.


  • Question 14

    State the meaning of inherited traits and acquired traits. Which of the two is not passes on the next generation? Explain with the help of an example.


  • Question 15

    How are fossils formed? Describe, in brief, two methods of determining the age of fossils.


  • Question 16

    If we pure-bred tall (dominant) pea plant with pure-bred dwarf (recessive) pea plant we will get pea plants of F1 generation. If we now self-cross the pea plant of F1 generation, then we obtain pea plants of F2 generation.

    (a) What do the plants of F2 generation look like?

    (b) State the ratio of tall plants to dwarf plants in F2 generation.

    (c) State the type of plants not found in F1 generation but appeared in F2 generation, mentioning the reason for the same.


  • Question 17

    A 5 cm tall object is placed perpendicular to the principle axis of a convex lens of focal length 12 cm. The distance of the object from the lens is 8 cm. Using the lens formula, find the position, size and nature of the image formed.


  • Question 18

    State the types of mirrors used for (i) headlights and (ii) rear view mirror, in cars and motorcycles. Give to justify your answer in each case.


  • Question 19

    An old man cannot see objects closer than 1 m from the eye clearly. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagram for the (i) defect of vision and also (ii) for its correction.


  • Question 20

    Name the oxidizing agent used for the conversion of ethanol to ethanoic acid. Distinguish between ethanol and ethanoic acid on the basis of (i) litmus test, (ii) reaction with sodium hydrogen carbonate.


  • Question 21

    List and explain in brief three methods of contraception.


  • Question 22

    Na, Mg and Al are the elements having one, two and three valence electrons respectively. Which of these elements (i) has the largest atomic radius, (ii) is least reactive? Justify your answer stating reason for each.


  • Question 23

    List the new Cartesian sign convention for reflection of light by spherical mirror. Draw a diagram and apply these conventions for calculating the focal length and nature of spherical mirror which forms a 1/3 times magnified virtual image of an object placed 18 cm in front of it.


    With the help of a ray diagram, state what is meant by refraction of light. State Snell’s law for refraction of light and also express it mathematically.

    The refractive index of air with respect to glass is 2/3 and the refractive index of water with respect to air is 4/3. If the speed of light in glass is 2 × 108 m/s, find the speed of light in (a) air, (b) water.


  • Question 24

    What are hydrocarbons? Write the name and general formula of (i) saturated hydrocarbons, (ii) unsaturated hydrocarbons, and draw the structure of one hydrocarbon of each type. How can an unsaturated hydrocarbon be made saturated?


    What are detergents chemically? List two merits and two demerits of using detergents for cleansing. State the reason for the suitability of detergents for washing, event in the case of water having calcium and magnesium ions.


  • Question 25

    Distinguish between unisexual and bisexual flowers giving one example of each. Draw a diagram showing process of germination of pollen grains on stigma and label the following parts:

    (a) Female germ cell

    (b) Male germ cell

    (c) Ovary


    Draw a diagram of human female reproductive system and label the part.

    (i) That produces eggs.

    (ii) Where fusion of egg and sperm take place.

    (iii) Where zygote is implanted.

    What happens to human egg when it is not fertilized?


  • Question 26

    The following figure illustrates binary fission in Amoeba in an incorrect sequence.

    The correct sequence is

    (A) III, II, IV, I

    (B) III, IV, II, I

    (C) II, III, IV, I

    (D) IV, III, II, I


  • Question 27

    From the following diagrams, select the correct ones showing stages of binary fission in Amoeba:

    (A) I, II, III

    (B) IV, II, III

    (C) V, II, III

    (D) IV, I, III


  • Question 28

    Following diagrams were drawn by different student on having seen prepared slides of budding in yeast.

    Correct diagrams are

    (A) I, II, III

    (B) II, III, IV

    (C) III, IV, V

    (D) I, IV, V


  • Question 29

    In which of the following figures is budding not shown?

    (A) I

    (B) II

    (C) III

    (D) IV


  • Question 30

    A student weighed some raisins and recorded the weight as ‘x’. She then soaked the raisins in distilled water. After about 2 hours she removed the raisins, wiped them dry and weighed again and recorded that as ‘y’. The percentage of water absorbed by raisins may be determined using the relationship






  • Question 31

    In the experiment for determining the percentage of water absorbed by raisins, we do the final weighing of the raisins after keeping them dipped in water for about one hour. For the accuracy of the result, the extra water from the surface of the soaked raisins is removed by

    (A) rubbing with cotton cloth

    (B) hot air blower

    (C) dry cotton wool

    (D) filter paper


  • Question 32

    On adding 2 mL acetic acid to 2 mL of water in a test tube, it was observed that

    (A) a clear and transparent solution is formed

    (B) a white precipitate is formed almost immediately

    (C) two separate layers were formed

    (D) a colourless and odourless gas is evolved


  • Question 33

    On adding acetic acid to sodium hydrogen carbonate in a test tube, a student observes

    (A) no reaction

    (B) a colourless gas with pungent smell

    (C) bubbles of a colourless and odourless gas

    (D) a strong smell of vinegar


  • Question 34

    Which one of the following are the correct observations about acetic acid?

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

    (B) It turns blue litmus red and smells like burning sulphur

    (C) It turns res litmus blue and smells like vinegar

    (D) It turns red litmus blue and has a fruity smell


  • Question 35

    The aqueous solutions of copper sulphate and zinc sulphate appear

    (A) blue and green respectively

    (B) green and colourless respectively

    (C) blue and brown respectively

    (D) blue and colourless respectively.


  • Question 36

    Solutions of copper sulphate, iron sulphate and zinc sulphate are prepared and marked I, II and III respectively. Few pieces of aluminium are added to each solutions. After some time a change will be observe in

    (A) I and II

    (B) II and III

    (C) III and I

    (D) All the three


  • Question 37

    Four students showed the following traces of the path of a ray of light passing through a rectangular glass slab.

    The trace most likely to be correct is that of student

    (A) I

    (B) II

    (C) III

    (D) IV


  • Question 38

    While performing the experiment on tracing the path of a ray of light through a rectangular glass slab, in which of the following experimental set-ups is a student likely to get best results? P1 and P2 are the positions of pins fixed by him.

    (A) I

    (B) II

    (C) III

    (D) IV


  • Question 39

    If you are to determine to focal length of a convex lens, you should have

    (A) a convex lens and a screen

    (B) a convex lens and a lens holder

    (C) a lens holder, a screen holder and a scale

    (D) a convex lens, a screen, holder for them and a scale


  • Question 40

    A student obtained a sharp inverted image of a distant tree on a screen placed in front of the concave mirror. He then removed the screen and tried to look into the mirror. He would now see

    (A) a very blurred image on the wall opposite to the mirror

    (B) an erect and magnified image of the tree in the mirror

    (C) no image as the screen has been removed

    (D) a highly diminished inverted image of the tree at the focus of the mirror.


  • Question 41

    A student has to determine the focal length of a concave mirror by obtaining the image of a distant object on a screen. For getting best result he should focus

    (A) a distant tree or an electric pole

    (B) a well-illuminated distant building

    (C) well-lit grills of the nearest window

    (D) a burning candle laced at the distant edge of the laboratory table

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