# 10th Science Paper Solutions Set 2 : CBSE Delhi Previous Year 2015

(i) The questions paper comprises two section, 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.
Q1 :

Write the name and formula of the 2nd member of homologous series having general formula CnH2n + 2.

CnH2n+2 is the general formula for the alkane series. The second member of the alkane family is ethane with the formula C2H6.

Q2 :

What is the magnification of the images formed by plane mirrors and why?

The magnification of the image formed by a plane mirror is 1. This is because the size of the image formed is equal to the size of the object.
Magnification, m=HiHo=1          (Hi=Ho)
Here, Hi is the height of the image and Ho is the height of the object.

Q3 :

What is meant by power of a lens?

The power of a lens (P) is the ability of the lens to converge or diverge an incident beam falling on it. It is expressed as the reciprocal of focal length (f).
The power of a lens (P) is given by
P=1f(in m)

Q4 :

Write two differences between binary fission and multiple fission in a tabular form.

Q5 :

(a) Why do we need to manage our resources carefully?

(b) Why management of natural resources requires a long term perspective?

Q6 :

List four measures that can be taken to conserve forests.

Q7 :

Na, Mg and Al are the elements of the same period of Modern Periodic Table 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 case.

Q8 :

From the following elements:
4Be; 9F; 19K; 20Ca
(i) select the element having one electron in 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).

Q9 :

What is meant by isomers? Draw the structures of two isomers of butane, C4H10. Explain why we cannot have isomers of first three members of alkane series.

Q10 :

What is the difference between the molecules of soaps and detergents, chemically? Explain the cleansing action of soaps.

Q11 :

What are sexually transmitted diseases. List two example of each diseases caused due to (i) bacterial infection and (ii) viral infection. Which device or devices may be used to prevent the spread of such diseases.

Q12 :

What is DNA copying? State its importance.

Q13 :

Explain budding in hydra with the help of labelled diagrams only.

Q14 :

What is speciation? List four factors responsible for speciation.

Q15 :

(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.

Q16 :

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?

Q17 :

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.

Q18 :

With the help of a labelled diagram, explain why the sun appears reddish at the sun-rise and the sun-set.

Q19 :

The image of a candle flame placed at a distance of 30 cm from a spherical lens is formed on a screen placed on the other side of the lens at a distance of 60 cm from the optical centre of the lens. Identify the type of lens and calculate its focal length. If the height of the flame is 3 cm, find the height of its image.

Q20 :

(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 2 Ã— 108 m/s, calculate the speed of light in:
(i) vacuum,
(ii) medium 'A'.

Q21 :

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.

Q22 :

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?

Q23 :

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.

Q24 :

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.

Q25 :

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

Q26 :

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 mirror of focal length 12 cm

Q27 :

After tracing the path of a ray of light through a glass prism a student marked the angle of incidence (âˆ i), angle of refraction (âˆ r) angle of emergence (âˆ e) and the angle of deviation (âˆ D) as shown in the diagram. The correctly marked angles are :

(A) âˆ i and âˆ r
(B) âˆ i and âˆ e
(C) âˆ i, âˆ e and âˆ D
(D) âˆ i, âˆ r and âˆ e

Q28 :

Four students P, Q, R and S traced the path of a ray of light passing through a glass slab for an angle of incidence 40Â° and measured the angle of refraction. The values as measured by them were 18Â°; 22Â°; 25Â° and 30Â° respectively. The student who has performed the experiment methodically is
(A) P
(B) Q
(C) R
(D) S

Q29 :

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

Q30 :

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

Q31 :

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

Q32 :

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

Q33 :

A student identified the various parts of an embryo of a gram seed and listed them as given below :
(I) Testa
(II) Plumule
(IV) Cotyledon
(V) Tegmen
Out of these the actual parts of the embryo are :
(A) I, II, III
(B) II, III, IV
(C) III, IV, V
(D) II, IV, V

Q34 :

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?

Q35 :

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.