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# Board Paper of Class 10 2017 Science (SET 3) - Solutions

(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 number 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.

• Question 1
Write the molecular formula of first two members of homologous series having functional group – OH.     VIEW SOLUTION

• Question 2
How does Plasmodium reproduce. Is this method sexual or asexual?     (1) VIEW SOLUTION

• Question 3
Why is a lake considered to be a natural ecosystem?  VIEW SOLUTION

• Question 4
An object is placed at a distance of 12 cm in front of a concave mirror of radius of curvature 30 cm. List four characteristics of the image formed by the mirror.  VIEW SOLUTION

• Question 5
How do advantages of exploiting natural resources with short term gains in mind differ from the advantages of managing our resources with a long-term perspective?  VIEW SOLUTION

• Question 6
What is meant by wildlife? How is it important for us?  VIEW SOLUTION

• Question 7
Complete the following chemical equations:     (3)
(i)
(ii) ${\mathrm{C}}_{2}{\mathrm{H}}_{5}\mathrm{OH}\underset{443\mathrm{K}}{\overset{\mathrm{Conc}.{\mathrm{H}}_{2}{\mathrm{SO}}_{4}}{\to }}$
(iii) VIEW SOLUTION

• Question 8
The molecular formula of two carbon compounds are C4H8 and C3H8. Which one of the two is most likely to show addition reaction? Justify your answer. Also give the chemical equation to explain the process of addition reaction in this case.    (3) VIEW SOLUTION

• Question 9
Write the names given to the vertical columns and horizontal rows in the Modern Periodic Table. How does the metallic character of elements vary on moving down a vertical column? How does the size of atomic radius vary on moving left to right in a horizontal row? Give reason in support of your answer in the above two cases.  VIEW SOLUTION

• Question 10
An element P (atomic number 20) reacts with an element Q (atomic number 17) to form a compound. Answer the following questions giving reason:

Write the position of P and Q in the Modern Periodic Table and the molecular formula of the compound formed when P reacts with Q.  VIEW SOLUTION

• Question 11
How did Mendel's experiments show that different traits are inherited independently? Explain.  (3) VIEW SOLUTION

• Question 12
Explain with the help of an example each, how the following provide evidence in favour of evolution:

(a) Homologous organs

(b) Analogous organs

(c) Fossils VIEW SOLUTION

• Question 13
What happens when:

(a) Accidently, Planaria gets cut into many pieces?

(b) Bryophyllum leaf falls on the wet soil?

(c) On maturation sporangia of Rhizopus bursts?  (3) VIEW SOLUTION

• Question 14
List any four steps involved in sexual reproduction and write its two advantages. VIEW SOLUTION

• Question 15
State the changes that take place in the uterus when:

(a) Implantation of embryo has occurred.

(b) Female gamete/egg is not fertilised.     VIEW SOLUTION

• Question 16
The image of a candle flame placed at a distance of 30 cm from a mirror is formed on a screen placed in front of the mirror at a distance of 60 cm from its pole. What is the nature of the mirror? Find its focal length. If the height of the flame is 2.4 cm, find the height of its image. State whether the image formed is erect or inverted. VIEW SOLUTION

• Question 17
Write about power of accommodation of human eye. Explain why the image distance in the eye does not change when we change the distance of an object from the eye?  VIEW SOLUTION

• Question 18
You have been selected to talk on 'ozone layer and its protection" in the school assembly on 'Environment Day.'

(a) Why should ozone layer be protected to save the environment?
(b) List any two ways that you would stress in your talk to bring in awareness amongst your fellow friends that would also help in protection of ozone layer as well as the environment. VIEW SOLUTION

• Question 19
How do Mendel's experiments show that      (5)
(a) traits may be dominant or recessive?
(b) Inheritance of two traits is independent of each other? VIEW SOLUTION

• Question 20
(a) Name the organ that produces sperms as well as secretes a hormone in human males. Name the hormone it secretes and write its functions.

(b) Name the parts of the human female reproductive system where fertilisation occurs.

(c) Explain how the developing embryo gets nourishment inside the mother's body.      VIEW SOLUTION

• Question 21
(a) Draw a ray diagram to explain the term angle of deviation.

(b) Why do the component colours of incident white light split into a spectrum while passing through a glass prism, explain.

(c) Draw a labelled ray diagram to show the formation of a rainbow.    (5) VIEW SOLUTION

• Question 22
(a) To construct a ray diagram we use two rays which are so chosen that it is easy to know their directions after reflection from the mirror. List two such rays and state the path of these rays after reflection in case of concave mirrors. Use these two rays and draw ray diagram to locate the image of an object placed between pole and focus of a concave mirror.

(b) A concave mirror produces three times magnified image on a screen. If the object is placed 20 cm in front of the mirror, how far is the screen from the object.  VIEW SOLUTION

• Question 23
Analyze the following observation table showing variation of image distance (v) with object distance (u) in case of a convex lens and answer the questions that follow, without doing any calculations:
 S. No. Object distance u (cm) Image distance v (cm) 1 −90 +18 2 −60 +20 3 −30 +30 4 −20 +60 5 −18 +90 6 −10 +100

(a) What is the focal length of the convex lens? Give reason in support of your answer.
(b) Write the serial number of that observation which is not correct. How did you arrive at this conclusion?
(c) Take an appropriate scale to draw a ray diagram for the observation at S. No. 4 and find the approximate value of magnification. VIEW SOLUTION

• Question 24
Soaps and detergents are both types of salts. State the difference between the two. Write the mechanism of the cleansing action of soaps. Why do soaps not form lather (foam) with hard water? Mention any two problems that arise due to the use of detergents instead of soaps.  (5) VIEW SOLUTION

• Question 25
The correct sequencing of angle of incidence, angle of emergence, angle of refraction and lateral displacement shown in the following diagram by digits 1, 2, 3 and 4 is:

(a) 2, 4, 1, 3
(b) 2, 1, 4, 3
(c) 1, 2, 4, 3
(d) 2, 1, 3, 4 VIEW SOLUTION

• Question 26
In the following diagram the correctly marked angles are :

(a) ∠A and ∠e

(b) ∠i, ∠A and ∠D

(c) ∠A ∠r and ∠e

(b) ∠A ∠r and ∠D VIEW SOLUTION

• Question 27
If you focus the image of a distant object, whose shape is given below, on a screen using a convex lens,

the shape of the image of this object on the screen would be:
(a)

(b)

(c)

(d)    VIEW SOLUTION

• Question 28
Three students A, B and C focused a distant building on a screen with the help of a concave mirror. To determine the focal length of the concave mirror they measured the distances as given below:
Student A : From mirror to the screen
Student B : From building to the screen
Student C : From building to the mirror
Who measured the focal length correctly ;
(a) Only A
(b) Only B
(c) A and B
(d) B and C VIEW SOLUTION

• Question 29
For demonstrating the preparation of soap in the laboratory which of the following combinations of an oil and a base would be most suitable?

(a) Mustard oil and calcium hydroxide

(b) Castor oil and calcium hydroxide

(c) Turpentine oil and sodium hydroxide

(d) Mustard oil and sodium hydroxide    (1) VIEW SOLUTION

• Question 30
You have four test tubes, A, B, C and D containing sodium carbonate, sodium chloride, lime water and blue litmus solutions respectively. Out of these the material of which test tube/ test tubes would be suitable for the correct test of acetic/ethanoic acid?
(a) only A
(b) A and B
(c) B and C
(d) A and D VIEW SOLUTION

• Question 31
A student took four test tubes P, Q, R and S and filled about 8 mL of distilled water in each. After that he dissolved an equal amount of Na2SO4 in P, K2SO4 in Q, CaSO4 in R and MgSO4 in S. On adding an equal amount of soap solution and shaking each test tube well, a good amount of lather will be obtained in the test tubes:   (1)

(a) P and Q
(b) P and R
(c) P, Q and S
(d) Q, R and S VIEW SOLUTION

• Question 32
Select the set of homologous organs from the following :

(a) Wings of pigeon and a butterfly

(b) Wings of bat and a pigeon

(c) Forelimbs of cow, a duck and a lizard

(d) Wings of butterfly and a bat VIEW SOLUTION

• Question 33
A student while observing an embryo of a gram seed listed various parts of the embryo as listed below :
Testa, Micropyle, Cotyledon, Tegmen, Plumule, Radicle. On examining the list the teacher commented that only three parts are correct. Select these three correct parts :

(a) Cotyledon, Testa, Plumule

(d) Cotyledon, Micropyle, Plumule VIEW SOLUTION

• Question 34
Name the type of asexual reproduction in which two individuals are formed from a single parent and the parental identity is lost. Write the first step from where such a type of reproduction begins. Draw first two stages of this reproduction.  (2) VIEW SOLUTION

• Question 35
A student places a candle flame at a distance of about 60 cm from a convex lens of focal length 10 cm and focuses the image of the flame on a screen. After that he gradually moves the flame towards the lens and each time focuses the image on the screen.

(a) In which direction-toward or away from the lens, does he move the screen to focus the image?
(b) How does the size of the image change?
(c) How does the intensity of the image change as the flame moves towards the lens?
(d) Approximately for what distance between the flame and the lens, the image formed on the screen is inverted and of the same size? VIEW SOLUTION

• Question 36
A gas is liberated immediately with a brisk effervescence, when you add acetic acid to sodium hydrogen carbonate powder in a test tube. Name the gas and describe the test that confirms the identity of the gas.    VIEW SOLUTION
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