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CBSE X - Set -2
SCIENCE PAPER 2012

Time allowed: 180 minutes; Maximum Marks: 90

General Instructions:
1)	All questions are compulsory.
2)	The question paper consists of 42 questions divided into 4 sections A, B, C and D. Section A comprises questions of 01 mark each, Section B comprises questions of 02 marks each, Section C comprises questions of 03 marks each and Section D comprises questions of 05 marks each.
3)	All questions in Section A are to be answered in one word, one sentence or as per the exact requirement of the question.
4)	There is no overall choice. However, internal choice has been provided wherever necessary.You have to attempt only one of the alternatives in all such questions.
5)	In question on construction, drawing should be near and exactly as per the given measurements.
6)	Use of calculators is not permitted.

SECTION A

Question 1

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

(i) HCOOH

(ii) C₂H₅CHO

Question 2

2. The sky appears dark instead of blue to an astronaut. State its reason.

Question 3

3. Depletion of ozone in the ozone layer is a cause for our worry. Why?

Question 4

4. Name two decomposers operating in our ecosystem.

Question 27

27. 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?

Options:
1. ∠i only
2. ∠i and ∠r
3. ∠i and ∠e
4. ∠r and ∠e

Question 28

28. 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:

Options:
1. I
2. II
3. III
4. IV

Correct Option:

Snell's law:

$\frac{\sin i}{\sin r} = \frac{n_{1}}{n_{2}}$

We know that n₂ = 1.5 (for glass) and n₁ = 1 (for air). When we substitute the values we get that the answer is D.

Question 29

29. 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:

Options:
1. mirror and the object
2. mirror and the screen
3. screen and the object
4. screen and the object and also mirror and the screen

Question 30

30. 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?

Options:
1. Move the screen slightly away from the mirror
2. Move the mirror slightly towards the screen
3. Move the screen and the mirror away from the object
4. Move the screen and the mirror towards the object

Question 31

31. 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

(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:

Options:
1. c, a, d, e, b
2. c, d, a, e, b
3. c, d, e, a, b
4. c, a, e, d, b

Question 32

32. 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:

Options:
1. gently rubbing with cotton cloth
2. hot air blower
3. dry cotton wool
4. filter paper

Question 33

33. 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:

Options:
1. $\frac{40 g - 35 g}{35 g} \times 100$
2. $\frac{40 g - 35 g}{40 g} \times 100$
3. $\frac{8 g - 5 g}{8 g} \times 100$
4. $\frac{8 g - 5 g}{5 g} \times 100$

Correct Option:

Absorption rate of water by raisins is done by using the formula

$\frac{W 2 - W 1}{W 1} \times 100$

W₂ - weight of wet raisin

W₁ - weight of dry raisin

Question 34

34. 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.

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

The correct observation(s) is/are:

Options:
1. A and C
2. B only
3. C and D
4. D, A and C

Question 35

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

Options:
1. b, c, d, e, a
2. b, e, d, c, a
3. b, d, e, c, a
4. b, d, c, e, a

Question 36

36. A student has to observe a permanent slide of binary fission in amoeba. Find the correct sequence of steps given below for focusing 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

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

Options:
1. d, c, b, a
2. a, b, d, c
3. a, d, c, b
4. a, c, d, b

Question 37

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

Options:
1. a
2. b
3. c
4. d

Question 38

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

Options:
1. It smells like vinegar and turns red litmus blue
2. It smells like onion and turns blue litmus red
3. It smells like orange and turns red litmus blue
4. It smells like vinegar and turns blue litmus red

Question 39

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

Options:
1. No reaction in the test tube
2. Colourless gas with pungent smell
3. Bubbles of a colourless and odourless gas
4. White fumes with smell of vinegar

Question 40

40. 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:

Options:
1. A layer of water over the layer of acetic acid
2. A layer of acetic acid over the layer of water
3. A precipitate settling at the bottom of the test tube
4. A clear colourless solution

Question 41

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

Options:
1. Pale green and light blue respectively
2. Light blue and dark green respectively
3. Dark blue and dark green respectively
4. Dark blue and pale green respectively

Question 42

42. 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:

Options:
1. Blue and green
2. Colourless and pale green
3. Colourless and light blue
4. Greenish and colourless

SECTION B

Question 5

5. State the modern periodic law for classification of elements. How many (i) groups and (ii) periods are there in the modern periodic table?

Question 6

6. An element 'M' has atomic number 11.

(a) Write its electronic configuration.

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

(d) Write the formula of its chloride.

Question 7

7. List two advantages of vegetative reproduction practiced in case of an orange plant.

Question 8

8. How does growing embryo get nutrition from the mother's blood?

Question 9

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.

Question 10

10. List four properties of the image formed by a convex mirror.

Question 11

11. List four advantages of water stored in the ground.

Question 12

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

Question 13

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

Question 25

25. 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 soaps are not considered suitable for washing where water is hard?

Question 26

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

Ethanol	Ethanoic acid
It is liquid at room temperature	It freezes in winter
It melts at 156K	It melts at 290 K
It boils at 351K	It boils at 391K

Ethanol	Ethanoic acid
A reaction with metallic sodium results in realsing of hydrogen gas	A reaction with metallic sodium does not yield any hydrogen gas
Ethanol do not reacts with sodium hydrogen carbonate	Ethanoic acid produces carbon dioxide gas when it reacts with sodium hydrogencarbonate
Ethanol reacts with Acidified KMnO₄ And oxidised into Ethanoic acid	Ethanoic acid has no reaction with acidified KMnO₄

SECTION C

Question 14

14. Define homologous series of organic compounds. List its two characteristics. Write the name and formula of the first member of the series of alkenes.

Question 15

15. 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.

Question 16

16. 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.

Question 17

17. State and describe in brief any three main factors responsible for the rise of a new species.

Question 18

18. 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.

Homologous organs	Analogous organs
Homologous organs are those organs which have same basic structure and origin but perform different functions.	Analogous organs are those organs that have the same function but are different in structure and origin.
Show divergent evolution.	Show convergent evolution.
Forelimbs of frogs and those of a human are homologous organs.	Wings of a bird and those of a bat are examples of analogous organs
Organisms have modified over time, the function of organs to better suit their environment.	The process of natural selection has made organisms use different organs for the same purpose to increase their chance of survival.

Question 19

19. 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?

Question 20

20. The image of a candle flame placed at a distance 30 cm from a spherical lens is formed on a screen placed at a distance of 60 cm from the lens. Identify the type of lens and calculate its focal length. If the height of the flame is 2.4 cm, find the height of its image.

The lens formula is given by

$\frac{1}{v}$ − $\frac{1}{u} = \frac{1}{f}$

Given:

u = − 30 cm

v = 60 cm

h = 2.4 cm

$\frac{1}{60}$ − $\frac{1}{- 30} = \frac{1}{f}$

$\frac{1 + 2}{60}$ $= \frac{1}{f}$ ⇒

Hence ⇒f = + 20 cm and since f is positive the lens is convex.

Magnification is given by

m = $\frac{v}{u}$ = $\frac{h'}{h}$

$\frac{h'}{2.4}$ = $\frac{- 60}{30}$

h' = −4.8cm

The image is inverted.

Question 21

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.

Common Mistakes To Avoid

How To Solve

Solution

Remember that a convex mirror has a wide field of view but can form only dimished images but a concave mirror can form magnified images.

A rear view mirror should be able to give a wide field of view. So a convex mirror is used as a rear view mirror. A shaving mirror should be able to magnify things and a concave mirror will serve this purpose.

(i) The mirrors preferred as rear view mirrors in vehicles are convex mirrors.
A convex mirror always forms erect and virtual images.

The mirror can cover larger area as the images formed are of smaller size.

(ii) The mirrors preferred as having mirrors are concave mirrors.

A concave mirror forms enlarged images which enables us to see the object clearly.

Image formed is always erect and virtual when object is near the mirror, which is true in this case.

Question 22

22. 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.

Common Mistakes To Avoid

How To Solve

Solution

Remember that person suffering from myopia can see only nearby objects clearly and cannot see distant objects clearly.

Recall the name of the defect as myopia. Draw the relevant ray diagrams.

The student is suffereing from myopia or short sightedness. He cannot see distant objects clearly. This defect can be corrected using a concave lens.

SECTION D

Question 23

23. 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.

Common Mistakes To Avoid

How To Solve

Solution

Reproductive process in plants should be exactly demarcated from reproductive process in animals.
OR

Male reproductive system shares common structures with that of excretory system. One should know the specific function of those structures in both the systems.

The process of pollination and fertilisation in plants are explained.
OR

Male reproductive organs and their functions are described.

Pollination:
This is the transfer of pollen grains from the anther to the stigma of the carpel aided by agents of pollination.

Fertilisation:

This involves the fusion of male germ cell with the female germ cell resulting in the formation of a single cell, the zygote. This process is also called as syngamy.

OR

1.Testes - A pair of testis, part of the male reproductive system, found in the scrotum forms the gonads in male. It produces sperms, the male gametes and male hormones like testosterone.

2.Seminal Vesicle - These are special reservoirs for the sperms produced by testes. The main purpose of the seminal vesicle is to secrete a fluid which nourishes the sperm. Sperms along with this nourishing fluid form semen. The semen consists of an alkaline fluid liquid that neutralises the acidic nature of vagina and hence helps in prolonging the life of the sperm.

3.Vas deferens - It is a tube that carries sperm from the testes. It continues from the epididymis as a tube and extends up forming ejaculatory duct.

4.Ureter - It is a part of urinary system which connects the kidney to the urinary bladder. Its primary purpose is to collect urine from the kidney and convey to urinary bladder.

5.Prostrate gland - It provides prostratic fluid that improves motility. This provides a chance for improving the life of the sperm.

Question 24

24. 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.

Common Mistakes To Avoid

How To Solve

Solution

Remember: Object distance is considered to be negative. Real magnified images are possible only with concave mirrors. Use scale to draw the ray diagrams and mark the arrows properly.

List the sign conventions for spherical mirrors. Using the given data draw the ray diagram following sign conventions and find the focal length. (OR) State Snell's law. Express it using symbols. Write the formula connecting the relative refractive index and speed of light in two media. State what is absolute refractive index. Using the given data and the formula, find the speed of light in vacuum and in water.

The Cartesian sign convensions are as follows.
(i) The object is always placed to the left of the mirror, i.e. the light from the object falls on the mirror from the left-hand side.

(ii) All distances parallel to the principal axis are measured from the pole of the mirror. (The principal axis is taken along the x-axis with pole as the origin.)

(iii) All the distances measured to the right of the pole are taken as positive while those measured to the left of the pole are taken as negative.

(iv) Distances measured perpendicular to and above the principal axis are taken as positive.

(v) Distances measured perpendicular to and below the principal axis are taken as negative.

Given:

Object distance u = −16 cm

Magnification m = − $\frac{v}{u}$

−3 = $- \frac{v}{- 16}$ = $\frac{v}{16}$

⇒ v = − 48 cm (image distance)

We have $\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$ (mirror formula)

$\frac{1}{f} = \frac{1}{- 48} + \frac{1}{- 16}$

⇒ f = −12 cm (focal length of the concave mirror)

OR

The law that defines the refractive index of one medium with respect to the another is called the Snell's law.

Snell’s law states that the ratio of the sine of the angle of incidence to the sine of angle of refraction is a constant.

Mathematically it can be expressed as follows:

$\frac{\sin i}{\sin r} = cons \tan t =$ n_a_b

where n_ab is the relative refractive index of medium B with respect to medium A. Suppose a ray of light is travelling from medium B into medium A. Let v_a be the speed of light in medium A and v_b 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 = $\frac{v_{b}}{v_{a}}$

If one medium (say B) is vacuum or air then the constant is named as absolute refractive index of medium A and is simply written as n_a.

The absolute refractive index of glass n_g= 3/2

The absolute refractive index of water n_w= 4/3

Speed of light in glass v_g = 2 × 10⁸ m/s

(i) Speed of light in vacuum c:

n_g = $\frac{c}{v_{g}}$

c = n_g × v_g

= (3/2) × 2 × 10⁸ m/s = 3 × 10⁸ m/s

(ii) Speed of light in water v_w:

$n_{w}$ = $\frac{c}{v_{w}}$

$v_{w}$ = $\frac{c}{n_{w}}$

= 3 × 10⁸ m/s / (4/3)

= 2.25 × 10⁸ m/s

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CBSE Class 10 - Science