Chapter 8: Organic Chemistry – Some Basic Principles and Techniques Assertion-Reason Questions | chemistry Class 11 CBSE

Chapter 8: Organic Chemistry – Some Basic Principles and Techniques Assertion-Reason Questions | chemistry Class 11 CBSE | ByteNotes.in

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 1

Logic Check

Assertion (A): The sp hybridised carbon is more electronegative than sp3 hybridised carbon. Reason (R): Greater s-character in the hybrid orbital means the electrons are held closer to the nucleus, increasing effective electronegativity.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 2

Logic Check

Assertion (A): Rotation about a carbon-carbon double bond is restricted. Reason (R): The sigma bond framework of C=C is rigid and does not allow rotation.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 3

Logic Check

Assertion (A): Bond-line structural formula does not show carbon or hydrogen atoms explicitly. Reason (R): In bond-line formulas, terminals represent CH3 groups and junctions represent carbon atoms bonded to appropriate numbers of hydrogens.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 4

Logic Check

Assertion (A): The tertiary carbocation (CH3)3C+ is more stable than the primary carbocation CH3CH2+. Reason (R): In (CH3)3C+, nine C-H bonds are available for hyperconjugation with the empty p orbital, providing greater stabilisation.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 5

Logic Check

Assertion (A): The methyl cation (CH3+) is the least stable carbocation. Reason (R): In CH3+, the vacant p orbital is perpendicular to the plane containing C-H bonds, preventing hyperconjugative overlap.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 6

Logic Check

Assertion (A): Homolytic cleavage of a covalent bond produces free radicals. Reason (R): In homolytic cleavage, both electrons of the shared pair go to one of the bonded atoms.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 7

Logic Check

Assertion (A): OH- is a nucleophile in its reaction with CH3Br. Reason (R): Nucleophiles are electron pair donors that attack electron-deficient centres.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 8

Logic Check

Assertion (A): The inductive effect decreases with increasing distance from the source. Reason (R): The inductive effect becomes negligibly small after about three bonds from the inducing group.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 9

Logic Check

Assertion (A): Benzene has uniform C-C bond lengths of 139 pm. Reason (R): Benzene is a resonance hybrid of two Kekule structures, resulting in full delocalisation of pi electrons over all six carbons.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 10

Logic Check

Assertion (A): The electromeric effect is a permanent effect. Reason (R): The electromeric effect is annulled as soon as the attacking reagent is removed from the reaction domain.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 11

Logic Check

Assertion (A): Sublimation can be used to purify naphthalene from a mixture containing sand. Reason (R): Naphthalene sublimes on heating and can be separated from non-sublimable impurities by condensing its vapours.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 12

Logic Check

Assertion (A): Fractional distillation is preferred over simple distillation for separating ethanol and water. Reason (R): Ethanol and water have boiling points that are too close for effective separation by simple distillation.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 13

Logic Check

Assertion (A): In TLC, a compound with a higher Rf value is more strongly adsorbed on the stationary phase. Reason (R): Greater adsorption means the compound travels less distance with the solvent, giving a lower Rf value.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 14

Logic Check

Assertion (A): Nitrogen, sulphur, and halogens in organic compounds cannot be detected directly by ionic reactions without prior sodium fusion. Reason (R): These elements exist in covalent form in organic compounds and must be converted to ionic form (NaCN, Na2S, NaX) by fusion with sodium before ionic detection is possible.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 15

Logic Check

Assertion (A): Kjeldahl's method cannot be used to estimate nitrogen in pyridine. Reason (R): The nitrogen in pyridine is present in a heterocyclic aromatic ring and does not convert to ammonium sulphate under Kjeldahl conditions.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 16

Logic Check

Assertion (A): Acetic acid is a stronger acid than ethanol. Reason (R): The acetate ion (CH3COO-) is stabilised by resonance delocalisation of the negative charge over two oxygen atoms, while the ethoxide ion (CH3CH2O-) has localised negative charge.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 17

Logic Check

Assertion (A): Cl3CCOOH is a stronger acid than ClCH2COOH. Reason (R): Three chlorine atoms exert a greater electron-withdrawing inductive effect, stabilising the carboxylate anion more effectively than one chlorine atom.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 18

Logic Check

Assertion (A): CCl4 does not give a white precipitate of AgCl when heated with AgNO3 solution. Reason (R): The C-Cl bonds in CCl4 are covalent and do not produce free Cl- ions in solution.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 19

Logic Check

Assertion (A): An organic liquid vaporises below its boiling point during steam distillation. Reason (R): In steam distillation, the mixture boils when the sum of the vapour pressures of water and the organic compound equals atmospheric pressure.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 20

Logic Check

Assertion (A): In paper chromatography, the stationary phase is the organic solvent used as eluant. Reason (R): Paper chromatography paper contains water trapped in its fibres, which acts as the stationary phase.

Reasoning Options

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Chapter 8: Organic Chemistry – Some Basic Principles and Techniques | Assertion-Reason

Assertion (A): The sp hybridised carbon is more electronegative than sp3 hybridised carbon. Reason (R): Greater s-character in the hybrid orbital means the electrons are held closer to the nucleus, increasing effective electronegativity.

Assertion (A): Rotation about a carbon-carbon double bond is restricted. Reason (R): The sigma bond framework of C=C is rigid and does not allow rotation.

Assertion (A): Bond-line structural formula does not show carbon or hydrogen atoms explicitly. Reason (R): In bond-line formulas, terminals represent CH3 groups and junctions represent carbon atoms bonded to appropriate numbers of hydrogens.

Assertion (A): The tertiary carbocation (CH3)3C+ is more stable than the primary carbocation CH3CH2+. Reason (R): In (CH3)3C+, nine C-H bonds are available for hyperconjugation with the empty p orbital, providing greater stabilisation.

Assertion (A): The methyl cation (CH3+) is the least stable carbocation. Reason (R): In CH3+, the vacant p orbital is perpendicular to the plane containing C-H bonds, preventing hyperconjugative overlap.

Assertion (A): Homolytic cleavage of a covalent bond produces free radicals. Reason (R): In homolytic cleavage, both electrons of the shared pair go to one of the bonded atoms.

Assertion (A): OH- is a nucleophile in its reaction with CH3Br. Reason (R): Nucleophiles are electron pair donors that attack electron-deficient centres.

Assertion (A): The inductive effect decreases with increasing distance from the source. Reason (R): The inductive effect becomes negligibly small after about three bonds from the inducing group.

Assertion (A): Benzene has uniform C-C bond lengths of 139 pm. Reason (R): Benzene is a resonance hybrid of two Kekule structures, resulting in full delocalisation of pi electrons over all six carbons.

Assertion (A): The electromeric effect is a permanent effect. Reason (R): The electromeric effect is annulled as soon as the attacking reagent is removed from the reaction domain.

Assertion (A): Sublimation can be used to purify naphthalene from a mixture containing sand. Reason (R): Naphthalene sublimes on heating and can be separated from non-sublimable impurities by condensing its vapours.

Assertion (A): Fractional distillation is preferred over simple distillation for separating ethanol and water. Reason (R): Ethanol and water have boiling points that are too close for effective separation by simple distillation.

Assertion (A): In TLC, a compound with a higher Rf value is more strongly adsorbed on the stationary phase. Reason (R): Greater adsorption means the compound travels less distance with the solvent, giving a lower Rf value.

Assertion (A): Kjeldahl's method cannot be used to estimate nitrogen in pyridine. Reason (R): The nitrogen in pyridine is present in a heterocyclic aromatic ring and does not convert to ammonium sulphate under Kjeldahl conditions.

Assertion (A): Acetic acid is a stronger acid than ethanol. Reason (R): The acetate ion (CH3COO-) is stabilised by resonance delocalisation of the negative charge over two oxygen atoms, while the ethoxide ion (CH3CH2O-) has localised negative charge.

Assertion (A): Cl3CCOOH is a stronger acid than ClCH2COOH. Reason (R): Three chlorine atoms exert a greater electron-withdrawing inductive effect, stabilising the carboxylate anion more effectively than one chlorine atom.

Assertion (A): CCl4 does not give a white precipitate of AgCl when heated with AgNO3 solution. Reason (R): The C-Cl bonds in CCl4 are covalent and do not produce free Cl- ions in solution.

Assertion (A): An organic liquid vaporises below its boiling point during steam distillation. Reason (R): In steam distillation, the mixture boils when the sum of the vapour pressures of water and the organic compound equals atmospheric pressure.

Assertion (A): In paper chromatography, the stationary phase is the organic solvent used as eluant. Reason (R): Paper chromatography paper contains water trapped in its fibres, which acts as the stationary phase.

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