# Science 31/3/3 2018-2019 CBSE (English Medium) Class 10 Question Paper Solution

Science [31/3/3]
Date & Time: 14th March 2019, 2:30 pm
Duration: 3h

(i) All Questions are Compulsary .

(ii) Internal Choice is given in Sections B ,C , D and E .

Section A
[1] 1

Define 1 kilowatt hour.

Concept: Electrical Power
Chapter: [0.12] Electricity
[1] 2

Generally, we do not clean natural ponds or lakes but an aquarium needs periodic cleaning. Why?

Concept: Ecosystem
Chapter: [0.15] Our Environment
Section B
[2] 3

List two causes of presbyopia. Draw labelled diagram of a lens used for the correction of this defect of vision.

Concept: Eye Defect and Its Correction: Myopia Or Near-sightedness
Chapter: [0.11] The Human Eye and the Colourful World
[2] 4

Show the formation of Na2O by the transfer of electrons.

Concept: Chemical Equation
Chapter: [0.01] Chemical Reactions and Equations
[2] 5
[2] 5.a

List in tabular form two differences between reflex action and walking.

Concept: Reflex and Reflex Action
Chapter: [0.07] Control and Co-ordination
OR
[2] 5.b

List in tabular form two differences between pepsin and trypsin.

Concept: Human Digestive System
Chapter: [0.06] Life Processes
Section C
[3] 6

Name the process used to harness nuclear energy these days. Explain it briefly. List two advantages of using nuclear energy in place of fossil fuels.

Concept: Nuclear Energy
Chapter: [0.14] Sources of Energy
[3] 7

Why are forests considered “biodiversity hot spots”? Suggest four approaches towards the conservation of forests.

Concept: Stakeholders of Forest
Chapter: [0.16] Sustainable Management of Natural Resources
[3] 8
[3] 8.a

What is atmospheric reflection? Explain with the help of a labelled diagram that the position of a star as seen by us is not its true position.

Concept: Refraction of Light
Chapter: [0.1] Light - Reflection and Refraction
OR
[3] 8.b

When do we consider a student sitting in the class to be myopic? List two causes of this defect. Explain using a ray diagram how this defect of eye can be corrected.

Concept: Eye Defect and Its Correction: Myopia Or Near-sightedness
Chapter: [0.11] The Human Eye and the Colourful World
[3] 9

Write the chemical formula of washing soda. How can it be obtained from baking soda? List two industries in which washing soda is used for other purposes than washing clothes.

Concept: Properties of Acids
Chapter: [0.02] Acids, Bases and Salts
[3] 10
[3] 10.a

Out of three metals P, Q and R, P is less reactive than Q and R is more reactive than P and Q both. Suggest an activity to arragne P, Q and R in order of their decreasing reactivity.

Concept: Acids
Chapter: [0.02] Acids, Bases and Salts
OR
[3] 10.b

Name the ore of mercury. With the help of balanced chemical equations, explain the process of extraction of mercury from its ore.

Concept: Difference Between Metals, Non-metals, Metalloids, and Noble Gases
Chapter:
[3] 11

(a) How is possible valency of an element determined from the electronic configuration of its atom ?

(b) Determine the valency of an element X whose atomic number is 15.

Concept: History of Periodic Table: Early Attempts at the Classification of Elements
Chapter: [0.05] Periodic Classification of Elements
[3] 12

What is haemoglobin? State the consequences of deficiency of haemoglobin in our bodies.

Concept: Blood Circulatory System in Human
Chapter: [0.06] Life Processes
[3] 13
[3] 13.a

Explain the following :

(a) Speciation

(b) Natural Selection

Concept: Evolution
Chapter: [0.09] Heredity and Evolution
OR
[3] 13.b

Mendel, in one of his experiments with pea plants, crossed a variety of pea plant having round seeds with one having wrinkled seeds. State Mendel’s observations giving reasons of F1 and F2 progeny of this cross. Also, list any two contrasting characters, other than round seeds of pea plants that Mendel used in his experiments.

Concept: Heredity
Chapter: [0.09] Heredity and Evolution
[3] 14

Explain the ways in which glucose is broken down in absence or shortage of oxygen.

Concept: Carbon: a Versatile Element
Chapter: [0.04] Carbon and its Compounds
[3] 15

List in tabular form three distinguishing features between cerebrum and cerebellum.

Concept: Reflex and Reflex Action
Chapter: [0.07] Control and Co-ordination
Section D
[5] 16
[5] 16.a

What is hydrocarbon? Give its one example.

Concept: Carbon: a Versatile Element
Chapter: [0.04] Carbon and its Compounds
[5] 16.b

Give the structural difference between saturated and unsaturated hydrocarbons with two examples each.

Concept: Carbon: a Versatile Element
Chapter: [0.04] Carbon and its Compounds
[5] 16.c

Name of the following compounds :

Concept: Carbon: a Versatile Element
Chapter: [0.04] Carbon and its Compounds
[5] 17
[5] 17.a

(a) What is double displacement reaction? Explain with an example.

(b) A small amount of quick lime is added to water in a beaker.

(i) Name and define the type of reaction that has taken place.

(ii) Write balanced chemical equation for the above reaction and the chemical name of the product formed.

(iii) List two main observations of this reaction.

Concept: Types of Chemical Change or Chemical Reaction - Direct Combination (or Synthesis) Reaction
Chapter: [0.01] Chemical Reactions and Equations
OR
[5] 17.b

(a) Design an acitivity to demonstrate the decomposition reaction of lead nitrate.

(b) Draw labelled diagram of the experimental set-up. List two main observations.

(c) Write balanced chemical equation for the reaction stating the physical state of the reactant and the products.

Concept: Difference Between Metals, Non-metals, Metalloids, and Noble Gases
Chapter:
[5] 18
[5] 18.a

List four characteristics of the image formed by a concave lens of focal length 20 cm when the object is placed at a distance of 40 cm from its optical centre.

Concept: Refraction of Light
Chapter: [0.1] Light - Reflection and Refraction
[5] 18.b

The size of image of an object by a convex lens of focal length 20 cm is observed to be reduced to  1/3 rd of its size . Find the distance of the object from the optical centre of the lens .

Concept: Refraction of Light
Chapter: [0.1] Light - Reflection and Refraction
[5] 19
[5] 19.a

Three resistors of resistances R1 , R2 and R are connected (i) in series, and (ii) in parallel. Write expressions for the equivalent resistance of the combination in each case.

Concept: Electricity
Chapter: [0.12] Electricity
OR
[5] 19.b

Two identical resistros of  12 Omega each are connected to a battery of 3V . Calculate the ratio of the power consumed by the resulting combinations with minimum resistance and maximum resistance.

Concept: Electricity
Chapter: [0.12] Electricity
[5] 19.c

Write the relation between resistance and electrical resistivity of the material of a conductor in the shape of a cylinder of length 'l'  and area of cross-section 'A' . Hence derive the S.I. unit of electrical resistivity.

Concept: Factors Affecting the Resistance of a Conductor
Chapter: [0.12] Electricity
[5] 19.d

Resistance of a metal wire of length 5 m is 100 Ω . If the area of cross - section of the wire is 3 × 10^-7  "m"^2 , Calculate the resistivity of the metal .

Concept: Factors Affecting the Resistance of a Conductor
Chapter: [0.12] Electricity
[5] 20
[5] 20.a

Name and state the rule of determine the direction of force experienced by a current carrying straight conductor placed in a uniform magnetic field which is perpendicular to it.

Concept: Force on a Current Carrying Conductor in a Magnetic Field
Chapter: [0.13] Magnetic Effects of Electric Current
[5] 20.b

Draw a labelled diagram of an electric motor.

Concept: Electric Motor
Chapter: [0.13] Magnetic Effects of Electric Current
[5] 21
[5] 21.a

What is reproduction? List its two types.

Concept: Human Reproductive System
Chapter: [0.08] How do Organisms Reproduce?
[5] 21.b

How are the modes of reproduction different in unicellular and multicellular organisms?

Concept: Human Reproductive System
Chapter: [0.08] How do Organisms Reproduce?
(OR)
[5] 21.c

What are Sexually Transitted Diseases (STD)? List two viral and two bacterial STDs.

Concept: Reproductive Health
Chapter: [0.08] How do Organisms Reproduce?
[5] 21.d

What is contraception ? List three reasons for adopting contraceptive methods.

Concept: Reproductive Health
Chapter: [0.08] How do Organisms Reproduce?
Section E
[2] 22
(OR)
[2] 22.a

In the expriment of preparing a temporary mount of a leaf peel to observe stomata, we use two liquids other than water. Name these two liquids and state when and why these liquids are used.

Concept: Mode of Nutrition in Plant - Heterotrophic Nutrition
Chapter: [0.06] Life Processes
[2] 22.b

List four precautions in proper sequence which we observe while preparing a temporary mount of a leaf peel.

Concept: Mode of Nutrition in Plant - Heterotrophic Nutrition
Chapter: [0.06] Life Processes
[2] 23

A student has set up "CO2 is released during respiration”. After about 1 hour he observes no change in the water level in the delivery tube. Write two possible resons for the failure of the experiment.

Concept: Respiration
Chapter: [0.06] Life Processes
[2] 24

Consider the sacle of voltmeter shown in the diagram and answer the following questions :

(a) What is the least count of the voltmeter?

(b) What is the reading shown by the voltmeter ?

(c) If the voltmeter is connected across a resistor of 20 Omega how much current is flowing through the resistor?

Concept: Ohm's Law
Chapter: [0.12] Electricity
[2] 25
(OR)
[2] 25.a

List in proper sequence the steps of the experiment for determining the approximate focal length of a given concave mirror by obtaining the image of a distant object.

Concept: Refraction of Light
Chapter: [0.1] Light - Reflection and Refraction
[2] 25.b

A student has to trace the path of a ray of light passing through a rectangular glass slab for four different values of angle of incidence.

(a) Write two important precautions for this experiment.

(b) List two conclusions the student will draw based on his experiment.

Concept: Concave Mirror
Chapter: [0.1] Light - Reflection and Refraction
[2] 26

List the conclusions you will draw while studying the following properties of ethanoic acid :

(a) Odour

(b) Solubility in water

(c) Effect on litmus paper

(d) Reaction with sodium hydrogen carbonate

Concept: Carbon: a Versatile Element
Chapter: [0.04] Carbon and its Compounds
[2] 27
[2] 27.a

What is observed after about 1 hour of adding the strips of copper and aluminium separately to ferrous sulphate solution filled in two beakers ? Name the reaction if any change in colour is noticed. Also, write chemical equation for the reaction.

Concept: Difference Between Metals, Non-metals, Metalloids, and Noble Gases
Chapter:
(OR)
[2] 27.b

A student wants to study a decomposition reaction by taking ferrous sulphate crystals. Write two precautions he must observe while performing the experiment.

Concept: Types of Chemical Change or Chemical Reaction - Decomposition Reactions
Chapter: [0.01] Chemical Reactions and Equations

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