CBSE Question Bank in

II

Science

CLASS

10 Features Strictly Based on the Latest CBSE Term-wise Syllabus Chapter Summary Very Short Answer Type Questions

Short Answer Type Questions Long Answer Type Questions Case Study Based MCQs

Comprehensive

CBSE Question Bank in

Science

Term–II (For Class X)

Comprehensive CBSE Question Bank in

Science Term–II (For Class X) (According to the Latest CBSE Examination Pattern)

By

Dr. N.K. Sharma Nutan Vidya Mandir Dilshad Garden Delhi

 

laxmi Publications (P) Ltd (An iso 9001:2015 company)

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Comprehensive CBSE Question Bank in Science–X (Term-II) Copyright © by Laxmi Publications Pvt., Ltd. All rights reserved including those of translation into other languages. In accordance with the Copyright (Amendment) Act, 2012, no part of this publication may be reproduced, stored in a retrieval system, translated into any other language or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise. Any such act or scanning, uploading, and or electronic sharing of any part of this book without the permission of the publisher constitutes unlawful piracy and theft of the copyright holder’s intellectual property. If you would like to use material from the book (other than for review purposes), prior written permission must be obtained from the publishers. Printed and bound in India Typeset at : Excellent Graphics, Delhi. New Edition ISBN : 978-93-93268-96-9 Limits of Liability/Disclaimer of Warranty: The publisher and the author make no representation or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties. The advice, strategies, and activities contained herein may not be suitable for every situation. In performing activities adult supervision must be sought. Likewise, common sense and care are essential to the conduct of any and all activities, whether described in this book or otherwise. Neither the publisher nor the author shall be liable or assumes any responsibility for any injuries or damages arising here from. The fact that an organization or Website if referred to in this work as a citation and/or a potential source of further information does not mean that the author or the publisher endorses the information the organization or Website may provide or recommendations it may make. Further, readers must be aware that the Internet Websites listed in this work may have changed or disappeared between when this work was written and when it is read.

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Contents Pages

Theme: Materials Unit I: Chemical Substances–Nature and Behaviour

1–40



1. Carbon and its Compounds (NCERT Textbook Chapter-4) 1



2. Periodic Classification of Elements (NCERT Textbook Chapter-5) 13

Theme: The World of Living Unit II: World of Living

41–81



3. How do Organisms Reproduce? (NCERT Textbook Chapter-8) 41



4. Heredity and Evolution (NCERT Textbook Chapter-9) 69

Theme: Natural Phenomena Unit IV: Effects of Current

82–151



5. Electricity (NCERT Textbook Chapter-12) 82



6. Magnetic Effects of Current (NCERT Textbook Chapter-13) 123

Theme: Natural Resources Unit V: Natural Resources

152–168

7. Our Environment (NCERT Textbook Chapter-15) 152

Syllabus Class X Evaluation Scheme Theory Units

Term-II

Marks

I

Chemical Substances-Nature and Behaviour: Chapter 4 and 5

10

II

World of Living: Chapter 8 and 9

13

IV

Effect of Current: Chapter 12 and 13

12

V

Natural Recources: Chapter 15

05

Total

40 TERM-II

Theme: Materials Unit I: Chemical Substances–Nature and Behaviour Chapter–4 Carbon and its Compounds Carbon compounds: Covalent bonding in carbon compounds. Versatile nature of carbon. Homologous series. Chapter–5 Periodic Classification of Elements Periodic classification of elements: Need for classification, early attempts at classification of elements (Dobereiner’s Triads, Newland’s Law of Octaves, Mendeleev’s Periodic Table), Modern periodic table, gradation in properties, valency, atomic number, metallic and nonmetallic properties. Theme: The World of the Living Unit II: World of Living Chapter–8 How do organisms reproduce? Reproduction: Reproduction in animals and plants (asexual and sexual) reproductive health-need and methods of family planning. Safe sex vs HIV/AIDS.Child bearing and women’s health. Chapter–9 Heredity and Evolution Heredity: Heredity; Mendel’s contribution- Laws for inheritance of traits: Sex determination: brief introduction.

Theme: Natural Phenomena Unit IV: Effects of Current Chapter–12 Electricity Ohm’s law; Resistance, Resistivity, Factors on which the resistance of a conductor depends. Series combination of resistors, parallel combination of resistors and its applications in daily life. Heating effect of electric current and its applications in daily life. Electric power, Interrelation between P, V, I and R. Chapter–13 Magnetic Effects of Current Magnetic Effects of Current: Magnetic field, field lines, field due to a current carrying conductor, field due to current carrying coil or solenoid; Force on current carrying conductor, Fleming’s Left Hand Rule, Electric Motor, Electromagnetic induction. Induced potential difference, Induced current. Fleming’s Right Hand Rule. Theme: Natural Resources Unit V: Natural Resources Chapter–15 Our Environment Our environment: Eco-system, Environmental problems, Ozone depletion, waste production and their solutions. Biodegradable and non-biodegradable substances.

THEME: MATERIALS UNIT I: CHEMICAL SUBSTANCES—NATURE AND BEHAVIOUR

CHAPTER 1: Carbon and its Compounds (NCERT Textbook Chapter-4) SUMMARY OF THE CHAPTER 1. Carbon is tetravalent and easily forms a large variety of compounds on combination with carbon and other atoms by sharing of electrons. It exhibits phenomenon of allotropy, i.e., exists in two or more forms in the same state. For example, graphite and diamond. 2. Covalent bond: When two atoms achieve stability by sharing of an electron pair, each contributes one electron to the electron pair. In this way, the atoms can be regarded as having acquired a noble gas configuration. 3. Covalent compounds: Some atoms share electrons among themselves or with other atoms to attain stable octet configuration. Bonds formed are covalent bonds and the compounds so formed are covalent compounds. Depending on the number of shared pair of electrons, there is single covalent bond, double covalent bond or triple covalent bond.

H

× ×

H

H—H Single covalent bond

4. 5.

6. 7.

×× ×O ×

×× ××

×× O× ×

O O Double covalent bond

×N ×

×× ×× ××

N× ×

N N Triple covalent bond

These compounds have low melting points and boiling points. They do not dissolve in water, do not conduct electricity and are directional in nature. Catenation is the property of carbon to get attached to other carbon atoms. Up to 60 carbon atoms are found to get attached in the shape of a ball (Fullerenes). Allotropy: When an element possesses two or more different forms in the same state, they are called allotropes and the phenomenon is known as allotropy. For example, diamond and graphite are the two allotropes of carbon. Fullerenes: Fullerenes are allotropes of carbon. For example, Buckminsterfullerene is an allotrope of carbon with 60 carbon atoms arranged in the shape of a football. Hydrocarbons: Compounds containing only carbon and hydrogen are called hydrocarbons.

1

2

Science–X

8. Saturated hydrocarbons: Compounds of carbon and hydrogen attached in chains, branches or rings, by single covalent bonds, for example, Alkanes (CnH2n + 2): methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10). 9. Unsaturated hydrocarbons are compounds of carbon and hydrogen with either carbon-carbon double bond (C == C) or carbon-carbon triple bond (C ≡≡ C) in their molecules. For example, Alkenes (CnH2n): ethene (C2H4), propene (C3H6), butene (C4H8). Alkynes (CnH2n _ 2): ethyne (C2H2), propyne (C3H4) and butyne (C4H6). 10. Functional groups: Groups which determine the chemical nature of an organic compound. In a hydrocarbon, one or more hydrogen atoms are replaced by another element or group. These confer specific properties to the compound regardless of the length and nature of chain and hence are called functional groups. Name of Functional Group Halo Alcohol

Formula of Functional Group —Cl, —Br, —I —OH

Aldehyde Ketone

Carboxylic acid

11. Alkyl radical: The group formed by removal of the hydrogen atom from an alkane molecule is called an alkyl radical or group. 12. Functional group: A group which determines the chemical nature of an organic compound is called a functional group. 13. Homologous series is a group or family of compounds which contain the same functional group but have different chain lengths. Two successive homologues differ by one carbon and two hydrogen atoms in their molecular formulae. 14. Isomerism: In carbon compounds, different compounds are formed with different structures but with the same molecular formula. These compounds are called isomers and the phenomenon is called isomerism. For example, butane (C4H10) can be written as: H3C—CH2—CH2—CH3 (n-butane) and H3C—CH—CH2 (iso-butane) CH3

1. VERY SHORT ANSWER TYPE QUESTIONS [1 Mark] 1. Write the molecular formula of first two members of homologous series having functional group –OH. Ans. CH3OH, C2H5OH

3

Carbon and its Compounds

2. Draw the structural formula of methanoic acid.

(CBSE 2016)

O

Ans. H—C

or

HCOOH

O–H

3. Carbon has four electrons in its valence shell. How does carbon attain stable electronic configuration? (CBSE 2016) Ans. Carbon is tetravalent because it has four valence electrons. In order to achieve noble gas configuration, it shares these electrons with four electrons of other atoms. 4. The formula of citric acid is as follows:

COOH CH2 H3C—C—COOH CH2

Ans. 5. Ans. 6. Ans. 7. Ans. 8. Ans. 9. Ans. 10. Ans. 11. Ans. 12. Ans.

COOH State the name of –COOH functional group in citric acid. (CBSE 2016) Carboxylic acid Which of the following belong to the same homologous series? C3H8,C4H8,C4H6,C3H6. (CBSE 2016) C3H6 and C4H8 belong to the same homologous series which is alkenes with general formula CnH2n. Which has a triple bond; C2H4, C3H4 and C3H6? (CBSE 2016) C3H4 has triple bond with the formula CH3C ≡≡ CH. The molecular formula of butane is C4H10. What is the formula of butene? (CBSE 2016) The formula of butene is C4H8. A compound with molecular formula C3H6O is used as a fuel. Identify the compound. (CBSE 2016) The compound is ethanol with formula C2H5OH. Write the names of the next homologous of CH3CH2OH and HCOOH. (CBSE 2015) Propanol and ethanoic acid respectively. Name the second member of alkyne family. Give its structure. (CBSE 2014) The second member of alkyne family is propyne. Its structural formula is H3C—C≡≡CH. List two characteristic feature of carbon which when put together give rise to a number of carbon compounds. (CBSE 2014) (i) Catenation (ii) Tetravalency State the valency of each carbon atom in (i) an alkane and (ii) an alkyne. (CBSE 2014) (i) Valency of carbon atom in an alkane is four. (ii) Valency of carbon atom in an alkyne is four.

4

Science–X

13. Write the molecular formula of benzene and state the number of double bonds in its structure. (CBSE 2014) Ans. (i) The molecular formula of benzene is C6H6. (ii) It contains three double bonds in its structure. 14. The molecular formula of ‘A ’ is C10H18 and ‘B’ is C18H36. Name the homologous series to which they belong? (CBSE 2014) Ans. ‘A’ belongs to alkyne and ‘B’ belongs to alkene. 15. The formula of a hydrocarbon is CnH2n. Name the family to which it belongs and also predict its nature. (CBSE 2013) Ans. The hydrocarbon belongs to alkene family. It is unsaturated in nature. 16. What do we get when ethanoic acid reacts with ethanol in the presence of concentrated sulphuric acid? (CBSE 2013) Ans. Ethyl ethanoate (CH3COOC2H5) is formed by esterification reaction. It has fruity smell. 17. Write the molecular formula of first two members of homologous series having functional group-Cl. (CBSE 2017) Ans. The general formula for the homologous series of functional group –Cl is CnH2n + 1Cl (a) CH3Cl (b) CH3CH2Cl 18. What would be the electron dot structure of carbon dioxide which has the formula CO2? Ans. The electron-dot formula of CO2 is given as: ×× O ××

×. ×.

C

.× .×

×× × O×

19. What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? Ans. The electron-dot structure of sulphur is made of eight atoms of sulphur in a ring as shown. S

S

S

S

S S

S

S

20. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us? Ans. Two properties of carbon which lead to the huge number of carbon compounds are: (i) Tetravalency (ii) Catenation

5

Carbon and its Compounds

2. SHORT ANSWER TYPE QUESTIONS [2 and 3 Marks] 1. Name the element, other than carbon which exhibits the property of catenation upto seven or eight atoms? Are these compounds stable? (CBSE 2016) Ans. Silicon. No they are very reactive. 2. What is meant by homologous series of carbon compounds? Write the general formula of (i) alkene, and (ii) alkynes. Draw the structures of the first member of each series to show the bonding between the two carbon atoms. (CBSE 2016) Ans. (a) A series of organic compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series. (b) All consecutive members of this series differ by – CH2 unit. (c) Physical properties show gradation but chemical properties are same. (i) CnH2n (ii) CnH2n – 2

H

H C

H

C

H—C

C—H

H

3. The general formula of three compounds A, B, and C is CnH2n. B has highest boiling point and C has lowest boiling point. (i) Mention the type of compounds A, B and C. (ii) Which of these has the minimum number of carbon atoms?

(CBSE 2016)

Ans. (i) Unsaturated hydrocarbons with double bond. (ii) Compound ‘C’ has minimum number of carbon atoms. 4. List two characteristics of covalent compounds. Ans. (i) Covalent compounds have low melting and boiling points. (ii) Covalent compounds do not conduct electricity.

(CBSE 2016)

5. How do diamond and graphite differ in their structures? Is their any effect of structures on the nature of these? (CBSE 2016) Ans. Diamond and graphite are the two crystalline allotropic forms of carbon. But they differ in their structures. In diamond, all the four valence electrons of carbon atom are involved in the covalent bond formation with the electrons of neighbouring carbon atoms. In graphite, only three electrons participate in the bond formation while the fourth electron is free. Diamond without any free electron is a poor conductor of electricity while graphite with free electrons available is a good conductor. 6. Why are alkanes regarded as saturated hydrocarbons while alkenes and alkynes as unsaturated hydrocarbons? (CBSE 2016) Ans. Alkanes contain C—C bonds in the molecules and normal tetrahedral bond angle of 109°28′ is not disturbed. On the other hand, both alkenes and alkynes have a multiple bond (>C = C< or – C ≡ C – bond). The tetrahedral bond angle is no longer present. These are under strain and therefore, unsaturated. 7. List four characteristics of homologous series. (CBSE 2015) Ans. (i) Same functional group. (ii) Similar chemical properties.

6

Science–X

(iii) Successive member differ by – CH2 unit/14u./ (iv) Gradation in physical properties. 8. State the meaning of functional group in a carbon compound. Write the functional group present in (i) ethanol and (ii) ethanoic acid and also draw their structures. (CBSE 2015) Ans. An atom or group of atoms which determine the chemical properties of organic compounds are called functional groups. They confer specific properties to the compound, regardless of the length and nature of the carbon chain. S.No.

Organic compound

Functional group

Structure

(i) (ii)

Ethanol Ethanoic acid

Alcohol (—OH) Carboxylic acid

CH3 — CH2 — OH CH3 — COOH

O —C—OH

9. Give the electron dot structure and structural formula of first member of alkene and alkyne families. (CBSE 2014)

H

H

:

:

H H Ans. (i) H : C :: C : H

or

H—C

C—H

Ethene

(ii) H : C :: : C : H or

H—C

C—H.

Ethyne

10. What is homologous series? Which two of the following organic compounds belong to the same homologous series? C2H6, C2H6O, C2H6O2, CH4O (CBSE 2013) Ans. For the definition of homologous series, consult text part. The compounds CH4O and C2H6O belong to the same homologous series known as alkanols. 11. State two characteristic features of carbon which when put together give rise to a large number of carbon compounds. (CBSE 2013) Ans. (i) The size of carbon atom is very small (Atomic radius boads = 77 pm) (ii) The strength of C–C bond is quite high (355 kJ mol–1) Therefore, any number of carbon atoms can be linked by covalent bonds. This self linking property is called catenation. 12. (a) Why are most carbon compounds poor conductors of electricity? (b) Write the name and structure of a saturated compound in which the carbon atoms are arranged in a ring. Give the number of single bonds present in this compound. (CBSE 2018) Ans. (a) In most of carbon compounds, all the electrons take part in the formation of bonds and electrons are not free to move. Therefore, most of carbon compounds are poor conductors of electricity.

7

Carbon and its Compounds

(b) One such saturated compound is cyclobutane and its structure is:

It has 12 single covalent bonds. 13. How many structural isomers can you draw for pentane? Ans. Three structural isomers can be drawn for pentane:

14. What will be the formula and electron dot structure of cyclopentane? Ans. The formula of cyclopentane will be C5H10. Its electron-dot structure is written as,

H H Or

15. Ans.

16. Ans.

H H

H C

C

C

C

C

H H H

H H What is a homologous series? Explain with an example. A homologous series is a group of compounds which contain the same functional group but different chain lengths. Thus, these have the same chemical properties but different physical properties. Two adjacent members of a homologous series differ by a CH2 unit. Examples CH3OH, C2H5OH, C3H7OH, C4H9OH and C2H4, C3H6, C4H8, C5H10 are members of the two same homologous series respectively. Draw the electron dot structure of ethyne and also draw its structural formula. Molecular formula of ethyne is C2H2. Electronic configuration of C = 2, 4 (valence electrons = 4) Electronic configuration of H = 1 (valence electrons = 1)

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