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# Science Delhi (Set 2) 2019-2020 CBSE Class 10 Question Paper Solution

Course
Science [Delhi (Set 2)]
Date: February 2020

(i) The question paper comprises three sections - A, B and C.
There are 30 questions in the question paper. All questions are compulsory.
(ii) Section A - a question no. 1 to 14 - all questions or part thereof are of one mark each. These questions comprise multiple-choice questions (MCQ), very short answer (VSA), and Assertion-Reason type questions. Answers 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- a 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.

Section A
[14]1
[1]1.1

Name the functional group present in propanone.

Concept: Versatile Nature of Carbon - Nomenclature of Carbon Compounds
Chapter: [1.01] Carbon Compounds
[1]1.2

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

Concept: The Bar Magnet
Chapter: [4.01] Magnetic Effects of Current
[1]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 Questions
Chapter: [2.02] Reproduction
[1]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]1.5
[1]1.5.1

The compound obtained on reaction of iron with steam is/are :

Fe2O3

Fe3O4

FeO

Fe2O3 and Fe3O4

Concept: Introduction to Our Environment
Chapter: [5.02] Our Environment
OR
[1]1.5.2

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:

iron

calcium

carbon

silicon

Concept: Bonding in Carbon - Covalent Bond
Chapter: [1.01] Carbon Compounds
[1]1.6
[1]1.6.1

The laws of reflection hold true for:

plane mirrors only

concave mirrors only

convex mirrors only

all reflecting surfaces

Concept: Light Reflection and Refraction Introduction
Chapter: [3] Natural Phenomena
OR
[1]1.6.2

When an object is kept within the focus of a concave mirror, an enlarged image is formed behind the mirror. This image is :

real

inverted

virtual and inverted

virtual and erect

Concept: Refraction of Light - Image Formation by Lenses - Concave Lens
Chapter: [3] Natural Phenomena
[1]1.7
[1]1.7.1

Choose the correct option from given alternative:
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]1.7.2

Choose the correct option from given alternative:
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: Resistance of a System of Resistors - Resistors in Series
Chapter: [4.02] Effects of Current
[1]1.8

The chemical formula for plaster of Paris is :

CaSO4. 2H2O

CaSO4. H2O

$\ce{CaSo4.1/2H2O}$

2CaSO4. H2O

Concept: Chemicals from Common Salt Introduction
Chapter: [1.04] Acids, Bases and Salts
[1]1.9

Choose the correct option from given alternative:
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: Chemical Reactions - Types of Chemical Reactions - Double Displacement
Chapter: [1.05] Chemical Reactions
[1]1.10

Baking soda is a mixture of:

Sodium carbonate and acetic acid

Sodium carbonate and tartaric acid

Sodium hydrogen carbonate and tartaric acid

Sodium hydrogen carbonate and acetic acid

Concept: Chemicals from Common Salt Introduction
Chapter: [1.04] Acids, Bases and Salts
[1]1.11

In an ecosystem, 10% of energy available for transfer from one trophic level to the next is in the form of:

heat energy

chemical energy

mechanical energy

light energy

Concept: Concept of Eco-System
Chapter: [5.02] Our Environment
[1]1.12

Soil fertility is determined by its ability to :

Decay organic matter

Hold organic matter

Hold water

Support life

Concept: Concept of Life Processes
Chapter: [2.04] Life Processes
[1]1.13

Two statements are given - one labeled Assertion (A) and the other labeled 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.

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: Versatile Nature of Carbon - Homologous Series
Chapter: [1.01] Carbon Compounds
[1]1.14

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.

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 - Nuclear Energy
Chapter: [5.03] Sources of Energy
Section B
[30]1.15
[3]1.15.1

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

Concept: Corrosion and Its Prevention
Chapter: [1.02] Metals and Non Metals
[3]1.16

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

Concept: Evolution and Classification - Tracing Evolutionary Relationships
Chapter: [2.01] Heredity and Evolution
[3]1.17
[3]1.17.1

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]1.17.2

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]1.18

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.

Concept: Some Natural Phenomena Due to Sunlight
Chapter: [3] Natural Phenomena
[3]1.19
[1.5]1.19.1

List in tabular form two differences between binary fission and multiple fission.

Concept: Reproduction - Modes of Reproduction Used by Single Organisms - Fission
Chapter: [2.02] Reproduction
[1.5]1.19.2

What happens when a mature spirogyra filament attains considerable length?

Concept: Reproduction - Modes of Reproduction Used by Multicellular Organisms - Fragmentation
Chapter: [2.02] Reproduction
[3]1.20
[3]1.20.1

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]1.20.2

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]1.21

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 to the first drop by drop to this solution, then in excess.

(i) How is a 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 the chemical equation of this reaction.

Concept: Important Carbon Compounds - Ethanol
Chapter: [1.01] Carbon Compounds
[3]1.22
[3]1.22.1

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?

Concept: Hormones in Animals
Chapter: [2.03] Control and Co-ordination in Animals and Plants
OR
[3]1.22.2

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

Concept: Reproduction - Modes of Reproduction Used by Multicellular Organisms - Regeneration
Chapter: [2.02] Reproduction
[3]1.23
[1.5]1.23.1

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.

Concept: Ohm’s Law
Chapter: [4.02] Effects of Current
[1.5]1.23.2

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.

Concept: Electric Potential Difference
Chapter: [4.02] Effects of Current
[3]1.24
[1.5]1.24.1

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

Concept: Heating Effect of Electric Current
Chapter: [4.02] Effects of Current
[1.5]1.24.2

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

Concept: Heating Effect of Electric Current
Chapter: [4.02] Effects of Current
[5]1.25

What is thermit process? Where is this process used? Write a balanced chemical equation for the reaction involved.

Concept: Balanced Chemical Equation
Chapter: [1.05] Chemical Reactions

Where does the metal aluminium, used in the process, occurs in the reactivity series of metals?

Concept: Metals and Nonmetals - Chemical Properties of Metals - Reactivity Series
Chapter: [1.02] Metals and Non Metals

Name the substances that are getting oxidised and reduced in the process.

Concept: Balanced Chemical Equation
Chapter: [1.05] Chemical Reactions
[5]1.26

What is an electromagnet? List any two uses.

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

Draw a labelled diagram to show how an electromagnet is made.

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

State the purpose of soft iron core used in making an electromagnet.

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

List two ways of increasing the strength of an electromagnet if the material of the electromagnet is fixed.

Concept: Electromagnetic Induction
Chapter: [4.01] Magnetic Effects of Current
[5]1.27
[5]1.27.1

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: Reflection of Light - Spherical Mirrors
Chapter: [3] Natural Phenomena
OR
[5]1.27.2

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]1.28

What is genetics?

Concept: Heredity - Inherited Traits
Chapter: [2.01] Heredity and Evolution

What are genes? Where are the genes located?

Concept: Evolution - Acquired and Inherited Traits
Chapter: [2.01] Heredity and Evolution

State and define three factors responsible for the rise of a new species.

Concept: Speciation
Chapter: [2.01] Heredity and Evolution
[5]1.29
[5]1.29.1

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]1.29.2

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: The Modern Periodic Table
Chapter: [1.03] Periodic Classification of Elements
[5]1.30
[5]1.30.1
[2.5]1.30.1.1

Why is there a difference in the rate of breathing between aquatic organisms and terrestrial organisms? Explain.

Concept: Nutrition - Nutrition in Human Beings
Chapter: [2.04] Life Processes
[2.5]1.30.1.2

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

Concept: Concept of Respiration
Chapter: [2.04] Life Processes
[5]1.30.2
[2.5]1.30.2.1

Name the organs that form the excretory system in human beings.

Concept: Concept of Life Processes
Chapter: [2.04] Life Processes
[2.5]1.30.2.2

Describe in brief how urine is produced in the human body.

Concept: Concept of Excretion
Chapter: [2.04] Life Processes

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