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Science Delhi(Set 3) 2019-2020 CBSE Class 10 Question Paper Solution

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SubjectScience
Year2019 - 2020 (February)
Science [Delhi(Set 3)]
Marks: 74Academic Year: 2019-2020
Date: February 2020
Duration: 3h

Read the following instructions very carefully and strictly follow them:
(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 parts thereof are of one mark each. These questions comprise 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. Answers 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. Answers 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 is 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.


SECTION-A
[1]1

Name a cyclic unsaturated carbon compound.

Concept: Versatile Nature of Carbon - Saturated and Unsaturated Carbon Compounds
Chapter: [1.01] Carbon Compounds
[1]2

State an important advantage of using alternating current (a.c.) over direct current (d.c.).

Concept: Electromagnetic Induction
Chapter: [4.01] Magnetic Effects of Current
[1]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 the 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.

Concept: Reproduction - Introduction
Chapter: [2.02] Reproduction
[1]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

Concept: Components of Eco System - Food Chains and Webs
Chapter: [5.02] Our Environment
[1]5

Which one of the following is responsible for the sustenance of underground water?

Loss of vegetation cover

Diversion for high water demanding crops

 Pollution from urban wastes

Afforestation

Concept: Natural Resources - Water for All - Dams
Chapter: [5.01] Management of Natural Resources
[1]6

Incomplete combustion of coal and petroleum :
(A) increases air pollution.
(B) increases the efficiency of machines.
(C) reduces global warming.
(D) produce poisonous gases.

(A) and (B)

(A) and (D)

(B) and (C)

(C) and (D)

Concept: Chemical Properties of Carbon Compounds - Combustion
Chapter: [1.01] Carbon Compounds
[1]7

When sodium hydrogen carbonate is added to ethanoic acid a gas evolves. Consider the following statements about the gas evolved?
(A) It turns lime water milky.
(B) It is evolved with brisk effervescence.
(C) It has a smell of burning sulfur.
(D) It is also a by-product of respiration.

(A) and (B) only

(B) and (D) only

(A), (C) and (D)

(A), (B) and (D)

Concept: Important Carbon Compounds - Ethanoic Acid (Acetic acid)
Chapter: [1.01] Carbon Compounds
[1]8

When a small amount of acid is added to water, the phenomena which occur are:
(A) Dilution
(B) Neutralization
(C) Formation of H3O+ ions
(D) Salt formation

 (A) and (C)

 (B) and (D)

 (A) and (B)

 (C) and (D)

Concept: Acid Or a Base in a Water Solution
Chapter: [1.04] Acids, Bases and Salts
[1]9
[1]9.1

A real image is formed by the light rays after reflection or refraction when they:
(A) actually meet or intersect with each other.
(B) actually converge at a point
(C) appear to meet when they are produced in the backward direction.
(D) appear to diverge from a point.
Which of the above statements are correct?

(A) and (D)

(B) and (D)

(A) and (B)

(B) and (C)

Concept: Light Reflection and Refraction Introduction
Chapter: [3] Natural Phenomena
OR
[1]9.2

Consider the following properties of virtual images:
(A) cannot be projected on the screen
(B) are formed by both concave and convex lens
(C) are always erect
(D) are always inverted

(A) and (D)

(A) and (B)

(A), (B) and (C)

(A), (B) and (D)

Concept: Representation of Images Formed by Spherical Mirrors Using Ray Diagrams - Concave Mirror
Chapter: [3] Natural Phenomena
[1]10
[1]10.1

At the time of short circuit, the electric current in the circuit :

vary continuously

does not change.

reduces substantially

increases heavily

Concept: Electric Current and Circuit
Chapter: [4.02] Effects of Current
OR
[1]10.2

Two bulbs of 100 W and 40 W are connected in series. The current through the 100 W bulb is 1A. The current through the 40W bulb will be:

0.4 A

0.6 A

0.8 A

1 A

Concept: Effects of Current Introduction
Chapter: [4.02] Effects of Current
[1]11
[1]11.1

Calcium oxide reacts vigorously with water to produce slaked lime.
\[\ce{CaO{(s)} + H2O(l) -> Ca(OH)2(aq)}\]
This reaction can be classified as:
(A) Combination reaction
(B) Exothermic reaction
(C) Endothermic reaction
(D) Oxidation reaction

(A) and (C)

(C) and (D)

(A), (C) and (D)

(A) and (B)

Concept: Chemical Properties of Acids and Bases
Chapter: [1.04] Acids, Bases and Salts
OR
[1]11.2

When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid so formed remains in the solution. The reaction is an example of a:

Combination reaction

Displacement reaction

Decomposition reaction

Double displacement reaction

Concept: Chemical Reactions - Types of Chemical Reactions - Double Displacement
Chapter: [1.05] Chemical Reactions
[1]12

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

(B) and (D)

(A) and (C)

only (B)

(B), (C) and (D)

Concept: Important Carbon Compounds - Ethanol
Chapter: [1.01] Carbon Compounds
[1]13

Two statements are given - one labelled Assertion (A) and the other labelled Reason (R).
Assertion (A): Esterification is a process in which a sweet-smelling substance is produced.
Reason (R): When esters react with sodium hydroxide an alcohol and sodium salt of carboxylic acid are obtained.

Both A and R are true and R is the correct explanation of the Assertion.

Both A and R are true but R is not the correct explanation of the Assertion.

A is true but R is false.

A is false but R is true.

Concept: Important Carbon Compounds - Ethanol
Chapter: [1.01] Carbon Compounds
[1]14

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

Assertion (A): A solar cooker cooks the meal due to the greenhouse effect.
Reason (R): The plane mirror is responsible for producing the greenhouse effect.

Both A and R are true and R is the correct explanation of the Assertion.

Both A and R true but R is not the correct explanation of the Assertion.

A is true but R is false.

A is false but R is true.

Concept: Alternative or Non-conventional Sources of Energy - Solar Energy
Chapter: [5.03] Sources of Energy
SECTION-B
[3]15
[1.5]15.1

Write the mathematical expression for Joule's law of heating,

Concept: Heating Effect of Electric Current
Chapter: [4.02] Effects of Current
[1.5]15.2

Compute the heat generated while transferring 96000 coulombs of charge in two hours through a potential difference of 40 V.

Concept: Electric Potential Difference
Chapter: [4.02] Effects of Current
[3]16

Draw a labeled diagram to show
(i) the reddish appearance of the sun at the sunrise or the sunset and

(ii) white appearance of the sun at noon when it is overhead.

Concept: Some Natural Phenomena Due to Sunlight
Chapter: [3] Natural Phenomena
[3]17
[2]17.1

Draw the structures for ethanol

Concept: Carbon and Compounds Question
Chapter: [1.01] Carbon Compounds
[1]17.1.1

Draw the structures for ethanol

Concept: Carbon and Compounds Question
Chapter: [1.01] Carbon Compounds
[1]17.1.2

 Draw the structures for ethanoic acid.

Concept: Carbon and Compounds Question
Chapter: [1.01] Carbon Compounds
[1]17.2

Why is the conversion of ethanol to ethanoic acid considered an oxidation reaction? Write the oxidizing agent used in the reaction involved.

Concept: Carbon and Compounds Question
Chapter: [1.01] Carbon Compounds
[3]18
[3]18.1

Name the parts (a) to (e) in the following diagram.

What is the term given to the sequence of events occurring in the diagram?

Concept: Coordination in Plants - Immediate Response to Stimulus
Chapter: [2.03] Control and Co-ordination in Animals and Plants
[3]18.2
OR
[1.5]18.2.1

What is tropism?

Concept: Coordination in Plants - Immediate Response to Stimulus
Chapter: [2.03] Control and Co-ordination in Animals and Plants
[1.5]18.2.2

How do auxins promote the growth of a tendril around a support?

Concept: Coordination in Plants - Movement Due to Growth
Chapter: [2.03] Control and Co-ordination in Animals and Plants
[3]19
[3]19.1

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

Concept: Some Natural Phenomena Due to Sunlight
Chapter: [3] Natural Phenomena
OR
[3]19.2

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?

Concept: Dispersion by a Prism
Chapter: [3] Natural Phenomena
[3]20

Define the term pollination. Differentiate between self-pollination and cross-pollination. What is the significance of pollination?

Concept: Reproduction in Human Beings
Chapter: [2.02] Reproduction
[3]21
[3]21.1

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

Concept: Chemicals from Common Salt - Sodium Hydroxide
Chapter: [1.04] Acids, Bases and Salts
OR
[3]21.2

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 that can be removed by it?

Concept: Chemicals from Common Salt - Washing Soda
Chapter: [1.04] Acids, Bases and Salts
[3]22

1 g of copper powder was taken in a China dish and heated. What change takes place on heating? When hydrogen gas is passed over this heated substance, a visible change is seen in it. Give the chemical equations of reactions, the name and the color of the products formed in each case.

Concept: Chemical Equation
Chapter: [1.05] Chemical Reactions
[3]23

The near point of the eye of a person is 50 cm. Find the nature and power of the corrective lens required by the person to enable him to see clearly the objects placed at 25 cm from the eye?

Concept: Defects of Vision and Their Correction
Chapter: [3] Natural Phenomena
[3]24

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

Concept: Versatile Nature of Carbon - Homologous Series
Chapter: [1.01] Carbon Compounds
Section C
[5]25
[5]25.1

Draw a ray diagram in each of the following cases to show the formation of image, when the object is placed :

(i) between the 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).

Concept: Refraction of Light - Image Formation in Lenses Using Ray Diagrams - Convex Lens
Chapter: [3] Natural Phenomena
OR
[5]25.2

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 the image in this case.

Concept: Refraction of Light - Image Formation by Lenses - Convex Lens
Chapter: [3] Natural Phenomena
[5]26
[2.5]26.1

What is the law of dominance of traits? Explain with an example.

Concept: Early Attempts at the Classification of Elements - Newlands’ Law of Octaves
Chapter: [1.03] Periodic Classification of Elements
[2.5]26.2

Why are the traits acquired during the life-time-of-an individual not inherited? Explain.

Concept: Heredity - Inherited Traits
Chapter: [2.01] Heredity and Evolution
[5]27
[5]27.1
[2.5]27.1.1

A gas is released during photosynthesis. Name the gas and also state the way by which the gas is evolved.

Concept: Renewable Versus Non-renewable Sources
Chapter: [5.03] Sources of Energy
[2.5]27.1.2

What are stomata? What governs the opening and closing of stomata?

Concept: Nutrition - Nutrition in Human Beings
Chapter: [2.04] Life Processes
OR
[5]27.2
[2.5]27.2.1

Draw a diagram of human alimentary canal and label - gall bladder, pancreas, liver and small intestine on it.

Concept: Nutrition - Nutrition in Human Beings
Chapter: [2.04] Life Processes
[2.5]27.2.2

Give two reasons to explain why the absorption of digested food occurs mainly in the small intestine.

Concept: Nutrition - Nutrition in Human Beings
Chapter: [2.04] Life Processes
[5]28

Carbon cannot reduce the oxides of sodium, magnesium, and aluminum to their respective metals. Why? Where are these metals placed in the reactivity series? How are these metals obtained from their ores? Take an example to explain the process of extraction along with chemical equations.

Concept: Important Carbon Compounds - Ethanol
Chapter: [1.01] Carbon Compounds
[5]29
[5]29.1

The position of certain elements in the Modern Periodic Table is shown below:

Using the above table answer the following questions giving reasons in each case :
(i) 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 the largest atomic size?
(v) To which family does H, C, and F belong?

Concept: Position of Elements and Trends in the Modern Periodic Table
Chapter: [1.03] Periodic Classification of Elements
OR
[5]29.2

Define the 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?

Concept: Position of Elements and Trends in the Modern Periodic Table
Chapter: [1.03] Periodic Classification of Elements
[5]30
[2.5]30.1

Explain with the help of the pattern of magnetic field lines the distribution of the magnetic field due to a current-carrying a circular loop.

Concept: Force on a Current- Carrying Conductor in a Magnetic Field
Chapter: [4.01] Magnetic Effects of Current
[2.5]30.2

Why is it that the magnetic field of a current-carrying coil having n turns, is 'n' times as large as that produced by a single turn (loop)?

Concept: Introduction of Magnetism
Chapter: [4.01] Magnetic Effects of Current

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