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# Board Paper of Class 10 2020 Science Delhi(Set 2) - Solutions

General Instructions:
(i) Question paper comprises three sections - A, B and C.
There are 30 questions in the question paper. All questions are compulsory.
(ii) Section A - question no. 1 to 14 - all questions or part thereof are of one mark each. These questions comprises multiple choice questions (MCQ), very short answer (VSA), and Assertion-Reason type questions. Answer to these questions should be given in one word or one sentence.
(iii) Section B - question no. 15 to 24 are short answer type questions, carrying 3 marks each. Answer to these questions should not exceed 50 to 60 words.
(iv) Section C - question no. 25 to 30 are long answer type questions, carrying 5 marks each. Answer to these questions should not exceed 80 to 90 words.
(v) Answer should be brief and to the point. Also the above mentioned word limit be adhered to as far as possible.
(vi) There is no overall choice in the question paper. However, an internal choice has been provided in some questions in each Section. Only one of the choices in such questions have to be attempted.
(vii) In addition to this, separate instructions are given with each section and question, wherever necessary.

• Question 1
Name the functional group present in propanone. VIEW SOLUTION

• Question 2
The change in magnetic field lines in a coil is the cause of induced electric current in it. Name the underlying phenomenon.
VIEW SOLUTION

• Question 3
The growing size of the human population is a cause of concern for all people. The rate of birth and death in a given population will determine its size. Reproduction is the process by which organisms increase their population. The process of sexual maturation for reproduction is gradual and takes place while general body growth is still going on. Some degree of sexual maturation does not necessarily mean that the mind or body is ready for sexual acts or for having and bringing up children. Various contraceptive devices are being used by human beings to control the size of population.
(a) List two common signs of sexual maturation in boys and girls.
(b) What is the result of reckless female foeticide?
(c) Which contraceptive method changes the hormonal balance of the body?
(d) Write two factors that determine the size of a population. VIEW SOLUTION

• Question 4
Human body is made up of five important components, of which water is the main component. Food as well as potable water are essential for every human being. The food is obtained from plants through agriculture.  Pesticides are being used extensively for a high yield in the fields. These pesticides are absorbed by the plants from the soil along with water and minerals and from the water bodies these pesticides are taken up by the aquatic animals and plants. As these chemicals are not biodegradables, they get accumulated progressively at each trophic level. The maximum concentration of these chemicals gets accumulated in our bodies and greatly affects the health of our mind and body.

(a) Why is the maximum concentration of pesticides found in human beings?
(b) Give one method which could be applied to reduce our intake of pesticides through food to some extent.
(c) Various steps in a food chain represent :

(a) Food web
(b) Trophic level
(c) Ecosystem
(d) Biomagnification

(d) With regard to various food chains operating in an ecosystem, man is a:

(a) Consumer
(b) Producer
(c) Producer and consumer
(d) Producer and decomposer

VIEW SOLUTION

• Question 5
The compound obtained on reaction of iron with steam is/are :
(a) Fe2O3
(b) Fe3O4
(c) FeO
(d) Fe2O3 and Fe3O4

OR

An element 'X' reacts with O2 to give a compound with a high melting point. This compound is also soluble in water. The element 'X' is likely to be:
(a) iron
(b) calcium
(c) carbon
(d) silicon VIEW SOLUTION

• Question 6
The laws of reflection hold true for:
(a) plane mirrors only
(b) concave mirrors only
(c) convex mirrors only
(d) all reflecting surfaces

OR

When an object is kept within the focus of a concave mirror, an enlarged image is formed behind the mirror. This image is :
(a) real
(b) inverted
(c) virtual and inverted
(d) virtual and erect VIEW SOLUTION

• Question 7
At the time of short circuit, the electric current in the circuit :
(a) vary continuously
(b) does not change
(c) reduces substantially
(d) increases heavily

OR

Two bulbs of 100 W and 40 W are connected in series. The current through the 100 W bulb is 1 A. The current through the 40 W bulb will be:
(a) 0.4 A
(b) 0.6 A
(c) 0.8 A
(d) 1A VIEW SOLUTION

• Question 8
The chemical formula for plaster of Paris is :

(a) CaSO4. 2H2O

(b) CaSO4. H2O

(c) ${\mathrm{CaSO}}_{4}·\frac{1}{2}{\mathrm{H}}_{2}\mathrm{O}$

(d) 2CaSO4. H2O VIEW SOLUTION

• Question 9
In a double displacement reaction such as the reaction between sodium sulphate solution and barium chloride solution:
(A) exchange of atoms takes place
(B) exchange of ions takes place
(C) a precipitate is produced
(D) an insoluble salt is produced
The correct option is:
(a) (B) and (D)
(b) (A) and (C)
(c) only (B)
(d) (B), (C) and (D) VIEW SOLUTION

• Question 10
Baking soda is a mixture of:
(a) Sodium carbonate and acetic acid
(b) Sodium carbonate and tartaric acid
(c) Sodium hydrogen carbonate and tartaric acid
(d) Sodium hydrogen carbonate and acetic acid VIEW SOLUTION

• Question 11
In an ecosystem, 10% of energy available for transfer from one trophic level to the next is in the form of:
(a) heat energy
(b) chemical energy
(c) mechanical energy
(d) light energy VIEW SOLUTION

• Question 12
Soil fertility is determined by its ability to :
(a) Decay organic matter
(b) Hold organic matter
(c) Hold water
(d) Support life VIEW SOLUTION

• Question 13

Two statements are given - one labelled  Assertion (A) and the other labelled Reason (R).
Assertion (A) : In a homologous series of alcohols, the formula for the second member is C2H5OH and the third member is C3H7OH.
Reason (R) : The difference between the molecular masses of the two consecutive members of a homologous series is 144.

Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
(a) Both A and R are true and R is the correct explanation of the Assertion.
(b) Both A and R are true but R is not the correct explanation of the Assertion.
(c) A is true but R is false.
(d) A is false but R is true.

VIEW SOLUTION

• Question 14
Two statements are given - one labelled Assertion (A) and the other labelled Reason (R).

Assertion (A) : In the process of nuclear fission, the amount of nuclear energy generated by the fission of an atom of uranium is so tremendous that it produces 10 million times the energy produced by the combustion of an atom of carbon from coal.
Reason (R) : The nucleus of a heavy atom such as uranium, when bombarded with low energy neutrons, splits apart into lighter nuclei. The mass difference between the original nucleus and the product nuclei gets converted to tremendous energy.

Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
(a) Both A and R are true and R is the correct explanation of the Assertion.
(b) Both A and R true but R is not the correct explanation of the Assertion.
(c) A is true but R is false.
(d) A is false but R is true. VIEW SOLUTION

• Question 15
What is "rusting"? Describe with a labelled diagram an activity to investigate the conditions under which iron rusts. VIEW SOLUTION

• Question 16
What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor. Justify your answer. VIEW SOLUTION

• Question 17
Why is Tyndall effect shown by colloidal particles? State four instances of observing the Tyndall effect.

OR

Differentiate between a glass slab and a glass prism. What happens when a narrow beam of (i) a monochromatic light, and (ii) white light passes through (a) glass slab and (b) glass prism? VIEW SOLUTION

• Question 18
Draw a labelled diagram to show (i) reddish appearance of the sun at the sunrise or the sunset and (ii) white appearance of the sun at noon when it is overhead. VIEW SOLUTION

• Question 19
(a) List in tabular form two differences between binary fission and multiple fission.

(b) What happens when a mature Spirogyra filament attains considerable length.

VIEW SOLUTION

• Question 20
List the important products of the Chlor-alkali process. Write one important use of each.

OR

How is washing soda prepared from sodium carbonate? Give its chemical equation. State the type of this salt. Name the type of hardness of water which can be removed by it? VIEW SOLUTION

• Question 21
3 mL of ethanol is taken in a test tube and warmed gently in a water bath. A 5% solution of alkaline potassium permanganate is added first drop by drop to this solution, then in excess.

(i) How is 5% solution of KMnO4 prepared?

(ii) State the role of alkaline potassium permanganate in this reaction. What happens on adding it in excess?

(iii) Write chemical equation of this reaction.

VIEW SOLUTION

• Question 22
A squirrel is in a scary situation. Its body has to prepare for either fighting or running away. State the immediate changes that take place in its body so that the squirrel is able to either fight or run?

OR

Why is chemical communication better than electrical impulses as a means of communication between cells in a multi-cellular organism? VIEW SOLUTION

• Question 23
(a) State the relation correlating the electric current flowing in a conductor and the voltage applied across it. Also draw a graph to show this. relationship.

(b) Find the resistance of a conductor if the electric current flowing through it is 0.35 A when the potential difference across it is 1.4 V.

VIEW SOLUTION

• Question 24
(a) Write the mathematical expression for Joule's law of heating,
(b) Compute the heat generated while transferring 96000 coulomb of charge in two hours through a potential difference of 40 V. VIEW SOLUTION

• Question 25
(a) What is thermit process? Where is this process used? Write balanced chemical equation for the reaction involved.
(b) Where does the metal aluminium, used in the process, occurs in the reactivity series of metals?
(c) Name the substances that are getting oxidised and reduced in the process. VIEW SOLUTION

• Question 26
(a)What is an electromagnet ? List any two uses.
(b) Draw a labelled diagram to show how an electromagnet is made.
(c) State the purpose of soft iron core used in making an electromagnet.
(d) List two ways of increasing the strength of an electromagnet if the material of the electromagnet is fixed. VIEW SOLUTION

• Question 27
Draw a ray diagram in each of the following cases to show the formation of image, when the object is placed :
(i) between optical centre and principal focus of a convex lens.
(ii) anywhere in front of a concave lens.
(iii) at 2F of a convex lens.
State the signs and values of magnifications in the above mentioned cases (i) and (ii).

OR

An object 4.0 cm in size, is placed 25.0 cm in front of a concave mirror of focal length 15.0 cm.
(i) At what distance from the mirror should a screen be placed in order to obtain a sharp image?
(ii) Find the size of the image.
(iii) Draw a ray diagram to show the formation of image in this case. VIEW SOLUTION

• Question 28
(a) What is genetics?
(b) What are genes? Where are the genes located?
(c) State and define three factors responsible for the rise of a new species. VIEW SOLUTION

• Question 29
The position of certain elements in the Modern Periodic Table are shown below.

Using the above table answer the following questions giving reasons in each case :
(1) Which element will form only covalent compounds?
(ii) Which element is a non-metal with valency 2?
(iii) Which element is a metal with valency 2?
(iv) Out of H, C and F which has largest atomic size?
(v) To which family does H, C and F belong?

OR

Define atomic size. Give its unit of measurement. In the modern periodic table what trend is observed in the atomic radius in a group and a period and why is it so? VIEW SOLUTION

• Question 30
(a) Why is there a difference in the rate of breathing between aquatic organisms and terrestrial organisms? Explain.

(b) Draw a diagram of human respiratory system and label - pharynx, trachea, lungs, diaphragm and alveolar sac on it.

OR

(a) Name the organs that form the excretory system in human beings.

(b) Describe in brief how urine is produced in human body.

VIEW SOLUTION
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