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CBSE 10 - Set - 2
SCIENCE PAPER 2014

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. Write the number of horizontal rows in the modern periodic table. What are these rows called?

Question 2

2. Name the information source for making proteins in the cells.

Question 3

3. List two measures that you would suggest for the better management of water resources.

Question 25

25. A student has obtained an image of a distant object on a screen to determine the focal length F1 of the given lens. His teacher, after checking the image, gave him another lens of focal length F2 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 :

Options:
1. Concave and F1 < F2
2. Convex and F1 < F2
3. Convex and F1 > F2
4. Concave and F1 > F2

Question 26

26. 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?

Options:
1. Virtual, inverted and diminished image in red shade
2. Real, erect and diminished image in pink shade
3. Real, inverted and diminished image in red shade
4. Virtual, erect and enlarged image in red shade

Question 27

27.

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 ?

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

Question 28

28.

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:

S. No.	Object distance (cm)	Image distance (cm)
1.	60	15
2.	48	16
3.	36	21
4	24	24
5.	18	36
6.	16	48

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.

Options:
1. 2
2. 3
3. 5
4. 6

Question 29

29.

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:

Options:
1. Towards the normal while entering the prism and away from the normal while emerging from the prism
2. away from the normal while entering the prism and towards the normal while emerging from the prism
3. Away from the normal while entering as well as while emerging from the prism
4. Towards the normal while entering as well as while emerging from the prism

Question 30

30.

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:

Options:
1. O, Y, Z and N,
2. P, Y, M and Z,
3. O, X, M and Z,
4. P, X, Z and N.

Question 31

31. 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?

Options:
1. Angle of incidence is greater than the angle of emergence.
2. Angle of emergence is smaller than the angle of refraction.
3. Emergent ray is parallel to the refracted ray.
4. Incident ray and emergent ray are parallel to each other.

Question 32

32.

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)?

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

Question 33

33. 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

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:

Options:
1. P and Q
2. Q and R
3. R and S
4. P and S

Question 34

34. Which one of the following pairs of vegetables is an example of homologous structures?

Options:
1. Potato and sweet potato
2. Carrot and radish
3. Carrot and tomato
4. Tomato and radish

Question 35

35. Identify the figures showing the process of budding in yeast.

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

Question 36

36. Study the following diagrams showing various stages of binary fission in Amoeba:

The correct sequence of these diagrams should be:

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

Question 37

37. 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?

Options:
1. X and Y
2. Y and Z
3. X and Z
4. only Z

Question 38

38. 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 after shaking its contents, what will you observe in the test tube after about 5 minutes?

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

Question 39

39. 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

Options:
1. Exothermic and the solution is alkaline
2. Endothermic and the solution is alkaline
3. Endothermic and the solution is acidic
4. Exothermic and the solution is acidic

Question 40

40. 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

Options:
1. Reduce the alkalinity of the soap
2. Reduce the acidity of the soap
3. Enhance the cleansing capacity of soap
4. Favour precipitation of soap

Question 41

41. A student takes about 6 ml of distilled water in each of the four test tubes P, Q, R and S. He then dissolves 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 and shakes its contents. The test tubes in which scum (insoluble substance) is formed with soap are:

Options:
1. P and Q
2. Q and R
3. R and S
4. R and S

Question 42

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 :

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

SECTION B

Question 4

4. List four modes of asexual reproduction.

Question 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 the angle of incidence and the angle of reflection on it.

Question 6

6. In some states of our country there is a ban on the use of polythene bags for shopping. Why? List three advantages of using jute or cloth bags over polythene bags.

Question 7

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

SECTION C

Question 8

8. "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?

Question 9

9. 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?

Question 10

10. (a) Write the names of those parts of a flower which serve the same function as the following do in the animals :

(i) testis,

(ii) sperm,

(iii) ovary,

(iv) egg

(b) State the function of flowers in the flowering plants.

Reproductive organs in animals	Reproductive organs in plants
Testis	Anther
Sperm	Pollen grains
Ovary	Ovary
Egg	Ova/Ovum

Question 11

11. (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.

Question 12

12. (a) Mendel crossed tall pea plants with dwarf pea plants in his experiment. Write his observations giving reason on the F₁ and F₂ generations.

(b) List any two contrasting characters other than height that Mendel used in his experiments in pea plants.

Character in a pea plant	Dominant character	Recessive character
Shape of the seed	Round (R)	Wrinkled (r)
Colour of cotyledons	Yellow (Y)	Green (y)

Question 13

13. State the laws of refraction of light. If the speed of light in vacuum is 3 × 10⁸ ms⁻¹, find the speed of light in a medium of absolute refractive index 1.5.

State of Refractive of ilght and calculate speed of light based on provided data using formula.

Refractive light = $\frac{Speed of the light in vacuum}{Speed of light in medium}$

laws of refraction:

First law of refraction:

The first law of refraction or snell’s law states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant.

$\frac{\sin i}{\sin r}$ = $n_{12}$

Where, $n_{12}$ is the relative refractive index of medium 1 with 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 passes from medium 1 to medium 2, then the refractive index of medium 1 with respect to medium 2 is expressed as:

$\frac{Speed of the light in medium 2}{Speed of the light in medium 1} = \frac{v_{2}}{v_{1}}$

Where $v_{2}$ and $v_{1}$ are speed of light in medium 2 and 1 respectively.

Speed of light in medium with refractive index 1.5 can be calculated as follows.

Speed of light in vaccum = 3 × 10⁸ m/s

$n_{m} = \frac{Speed of the light in vacuum}{Speed of the light in medium} = 1.5 \Rightarrow 1.5 = \frac{3 \times 10^{8} m/s}{Speed of the light in medium}$

Speed $of the light in$ medium = $\frac{3 \times 10^{8} m/s}{1.5}$

Speed of light in a medium that has refractive index of 1.5 is equal to 2 $\times 10^{8}$ m/s

Where is the relative refractive index of medium 1 with medium 2.

Question 14

14.
A spherical mirror produces an image of magnification −1 on a screen placed at a distance of 40 cm from the mirror:

(i) Write the type of mirror.

(ii) What is the nature of the image formed?

(iii) How far is the object located from the mirror?

(iv) Draw the ray diagram to show the image formation in this case.

Common Mistakes To Avoid

How To Solve

Solution

Know difference between the convex and concave mirrors

Based on the knowledge of the reflection of light by the spherical mirrors

(i) Concave

(ii) Real, inverted and of the same size as the object

(iii) Here the object distance = image distance as the object is placed on the center of curvature. Therefore the object is placed at 40 cm from the mirror.

(iv)

Question 15

15. Why does the sun seem to rise two minutes before the actual sunrise and set two minutes after the actual sunset ? Explain with the help of labelled diagram.

Common Mistakes To Avoid

How To Solve

Solution

Know the difference among, reflection, refraction and scattering

To answer this question the knowledge of diffraction and scattering of ligh is needed.

The Sun is visible to us two minutes before the sunrise and two minutes after the sunset because of the bending of light due to atmospheric refraction. The atmosphere consists of various layers of air with different densities. As the light moves through these layers refraction takes place, so the light bends and it appears that the sun is rising before it actually rises on the horizon. The same thing applies for a sunset as well.
As the sunrise takes place when the Sun is just above the horizon we see the Sun about two minutes before it is actually above the horizon, due to atmospheric refraction of light.

As the sunset takes place when the Sun is just below the horizon, the Sun appears to be above the horizon due to the atmospheric refraction. This occurs becasue the light moves from less dense air to more dense air and gets refracted towards the normal.

Question 16

16. 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

Common Mistakes To Avoid

How To Solve

Solution

Generally addition reactions occur in unsaturated hydrocarbons. Both alkenes and alkynes are comes under unsaturated hydrocarbons. Some times student remember alkenes only. but they should consider the alkynes also.

Students commit mistakes while writing the general formulae of alkenes and alkynes.

First write an alkane with two carbon atoms.Try to write the general formula of of that alkane.
Then reduce two hydrogens from that general formula you will get the general formula for alkenes.

From this alkenes remove two hydrogen atoms you will get the general formula for alkynes.

In addition reaction unsaturated hydrocarbons are converted into saturated hydrocarbons.

To get an alkane from alkene add 1 mole of hydrogen (two hydrogen atoms) in the presence of a catalyst.

To get an alkane from alkyne add 2 moles of hydrogen (four hydrogen atoms) in the presence of a catalyst.

Hydrocarbons in which an addition reaction with hydrogen can take place are alkenes and alkynes

General formula of Alkene - C_nH_2n

General formula of Alkene Alkyne - C_nH_2n-2

For an addition reaction to occur double and triple bonds must exist between carbon atoms in the hydrocarbon chain. Nickel or platinum is used as catalyst.

The reaction is represented as

Question 17

17. State the meaning of the functional group in an organic compound. Write the formula of the functional group present in alcohols, aldehydes, ketones and carboxylic acids.

Common Mistakes To Avoid

How To Solve

Solution

While writing the functional groups of different compounds instead of writing formula of one compound they may write the formula of other compound.

Students should remember the formulas of all functional group.

An atom or a group of atoms bonded to a carbon chain is commonly referred to as a functional group. It plays a large role in defining the chemical property of the organic compound.
Compound Functional group
Alcohol -OH
Aldehyde -CHO
Ketone >CHO
Carboxylic acid -COOH

Question 18

18. (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?

Common Mistakes To Avoid

How To Solve

Solution

There is a chance that students may think valency and valence electrons both are same. But both are different.
Students may think Atomic number increases from left to right so atomic size also increases. But this is not correct.

Students may think while moving left to right in a periodic table the group number increases so valency also increases. But this is not correct.

In group top to bottom number of shells increases relate this sentence to atomic size .
In period while moving from left to right there is no change in the number of shells. But electrons are added to the same shell. Hence nuclear attractions on the valence electrons increases. Relate this sentence to atomic size.

In group top to bottom there is no change in the valency but in period when we move from left to right valency is changed.

(a)
(i)The combining capacity of an atom or the number of unpaired electrons in the outermost shell of the atom is called valency

(ii) Atomic size is the distance measured from the outermost shell of an atom to the centre of the nucleus.

(b)

When we move from left to right along a period in the modern periodic table,

Valency - increases till 4 and then decreases.

Valency is equal to the number of unpaired electrons in the outermost shell of the atom known as valence electrons if valence electrons is less than or equal to 4.

Valency = 8 - number of valence electron, if number of valence electrons is more than 4

Atomic size decreases across a period. In a period when we move fron left to right the number of the valence shells do not vary but electrons are added by one unit which increases the nuclear charge. This decrease atomic size.

Question 19

19. Consider two elements 'A' (Atomic number 17) and 'B' (Atomic number 19) :
(i) Write the positions of these elements in the modern periodic table giving justification.

(ii) Write the formula of the compound formed when 'A' combines with 'B.'

(iii) Draw the electron dot structure of the compound and state the nature of the bond formed between the two elements.

Common Mistakes To Avoid

How To Solve

Solution

Assigning position to an element in periodic table is difficult.
While writing the valency there is a possibility to commit a mistake.

Write the electronic configuration of elements.Find the valence electrons.The number of valence electrons is equal to its group number.The valence shell or outer most shell number is equal to its period number.
Find the valancies of elements and write the formula of compound formed when A combines with B.

Element Period Group
A 3 17
B 4 1

Atomic number of A is 17

Electronic configuration of A = 2,8,7. Valence electrons present in atom A = 7

Valency of A = 8-7=1

The atomic number of atom B is 19

Electronic configuration of B = 2,8,8,1. valence valence electrons of B is 1.

valency of B =1

2015-03-10

The bond formed between A and B is ionic bond.

Generally a metal and a non-metal combine by means of an ionic bond.

Compound	Functional group
Alcohol	-OH
Aldehyde	-CHO
Ketone	>CHO
Carboxylic acid	-COOH

Element	Period	Group
A	3	17
B	4	1

SECTION D

Question 20

20. State the reason why carbon can neither form C⁴⁺ cations nor C⁴⁻ anions but forms covalent compound. Also state the reason to explain why covalent compounds:
(i) are bad conductors of electricity.

(ii) have low melting and boiling points.

Common Mistakes To Avoid

How To Solve

Solution

There is a chance that all the covalent compounds are bad conductors of electricity and possessing low melting and boiling points. But covalent compounds also posses high melting and boiling points in diamond and even good conductors of electricity in graphite form.

student has to study how carbon form bonds,by loosing,by gaining or by sharing electrons.While studying they should focus on reasons why carbon forms covalent compounds why not ionic compounds.
While studying the properties of covalent compounds student should know the reasons also.

Carbon has an atomic number of 6.
The electronic configuration of carbon is 2,4.

When we look at the electronic configuration of carbon, it is clear that it has to either gain or lose four electrons, to attain noble gas configuration. Suppose carbon gains four electrons it would form a C^-4 ion. It is unable to hold four extra electrons. Meaning, it would be difficult for the six protons to hold the ten electrons.

Suppose it loses four electrons it would form a C⁺⁴ cation which is again a difficult task. It would require a great deal of energy to remove four electrons leaving the cation with six protons in the nucleus and holding only two electrons. This makes either of these possibilities is difficult.

Carbon overcomes this difficulty by sharing its electrons with other atoms of carbon or with atoms of other elements. sharing of electrons results in a covalent bond and the shared electrons belong to either of the atoms, this sharing helps in achieving noble gas configuration.

(i)Covalent compounds don’t have free electrons. Hence they are bad conductors of electricity.

The intermolecular force of attraction in a covalent compound is weak and hence they have low boiling point and melting point.

Question 21

21. (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.

Common Mistakes To Avoid

How To Solve

Solution

The phenomenon of reproduction in animals should be exactly known in order to name the parts of the reproductive system.

Labelled diagram of female reproductive system is to be given. Concept of pregnancy and the processes after fertilisation are to be discussed.

(a)

(i) The organ that produces eggs - Ovary

(ii) The place where fusion of eggs and sperm takes place - Fallopian tube

(iii) The place where zygote is implanted - Uterus

Diagram of the female reproductive system

(b)

The zygote after it gets fertilised in the fallopian tube repeatedly divides to form an embryo which travels down to get implanted in the walls of the uterus or endometrium by the process of implantation. The placenta is a connective tissue established between foetus and the mother. It provides a large surface area for the nutrients and oxygen to pass from mother to the embryo.

This is the beginning of pregnancy.

As the months proceed, there are different changes observed in the embryo which gets itself transformed into foetus by giving rise to organs. Fully formed foetus is delivered out by the proces of parturition.

Question 22

22. (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?

Common Mistakes To Avoid

How To Solve

Solution

The phenomenon of reproduction in plants should be exactly demarcated from that of reproduction in animals.

Listing the examples of unisexual and bisexual flowers. Post fertilisation changes are explained. Restoration of amount of DNA after the process of reproduction is explained.

(a)Water melon, papaya, cucumber are some of the examples of unisexual flowers.

Rose, hibiscus, lily are some of the examples of bisexual flowers.

(b)Changes in a flower after fertilisation are termed to be post fertilisation changes.

i)A fertilised ovule transforms into a seed with embryo enclosed in it. The nourishing material present in the ovule is retained by cotyledons of the seed. The integuments of the ovule form the thick seed coat.

ii)Mature ovary develops into a fruit enclosing the seed in most cases.

iii)The accessory appendages like sepals, petals, stamens, styles and stigma usually fall off after fertilisation except in certain rare cases.

(c) DNA in the nucleus of the cell stores the the genetic information which is to be transferred to the offspring during reproduction.

Male gametes are haploid containing exactly half amount of DNA. Female gametes are also haploid containing exactly half amount of DNA.

During fertilisation, the nuclei of male and female fuse to form a diploid zygote thereby combining the amount of DNA present in them on a total. Hence the amount of DNA remains constant.

Question 23

23. (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?

Common Mistakes To Avoid

How To Solve

Solution

Caution: Cataract is not a refractive defect

(a)Myopia, Hypermetropia, Presbyopia are the three common refractive defects of vision. To correct Myopia or short-sightedness - Use appropriate concave lenses, Hypermetropia or long sightedness is corrected by using convex lenses of appropriate power and Presbyopia is corrected using bifocal lenses of appropriate power.
(b)Students can easily influence their family members to donate their eyes after their death. By making people aware and by registering to donate their eyes, students can play a very active role in reducing corneal blindness in the world.

Question 24

24.
A student wants to project the image of a candle flame on the walls of the school laboratory by using a mirror.

(a) Which type of mirror should he use and why?

(b) At what distance, in terms of focal length 'f' of the mirror, should he place the candle flame to get the magnified image on the wall?

(c) Draw a ray diagram to show the formation of the image in this case.

(d) Can he use this mirror to project a diminished image of the candle flame on the same wall? State 'how' if your answer is 'yes' and 'why not' if your answer is 'no.'

Common Mistakes To Avoid

How To Solve

Solution

Avoid confusion with convex, concave mirrors.

(a) As the plane mirror and convex mirror form onyly virtual images which cannot be caught onto the screen like a wall, we need to use the concave mirror to project the image of a candle flame on the walls of the school laboratory.
(b) The concave mirror forms magnified and real inverted image on the screen if the candle flame should be placed between the focus and centre of curvature of the mirror.

(c) Recall the rules to draw the ray diagrams for the images formed by a concave mirror.

(d) We have to answer whether this mirror forms the diminished image on the screen or not based on the knowledge of images formed by the coincave mirror.

(a) A concave mirror produces real images and hence it should be used.

(b) The candle flame should be placed between the focus and centre of curvature of the mirror.

(c)

(d) Yes, If the candle flame is placed at a long distance (infinity)it is possible to get the diminished image of the candle flame on the wall.

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CBSE Class 10 - Science

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