Chapter 8: Aldehydes, Ketones and Carboxylic Acids Assertion-Reason Questions | chemistry Class 12 CBSE

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 1

Logic Check

Assertion (A): Aldehydes are more reactive than ketones toward nucleophilic addition reactions. Reason (R): In aldehydes, only one alkyl group is attached to the carbonyl carbon, resulting in less steric hindrance and higher electrophilicity of the carbonyl carbon.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 2

Logic Check

Assertion (A): Benzaldehyde does not give a positive Fehling's test. Reason (R): Benzaldehyde lacks an alpha-hydrogen atom.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 3

Logic Check

Assertion (A): Carboxylic acids are stronger acids than phenols. Reason (R): The carboxylate ion has the negative charge delocalised over two equivalent electronegative oxygen atoms, making it more stable than the phenoxide ion.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 4

Logic Check

Assertion (A): Methanal (formaldehyde) is a gas at room temperature. Reason (R): Methanal has a very low molecular mass and lacks significant intermolecular forces.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 5

Logic Check

Assertion (A): The Cannizzaro reaction occurs only with aldehydes that have no alpha-hydrogen. Reason (R): Aldehydes with alpha-hydrogen prefer aldol condensation over disproportionation.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 6

Logic Check

Assertion (A): Carboxylic acids boil at higher temperatures than alcohols of comparable molecular masses. Reason (R): Carboxylic acids exist as dimers through intermolecular hydrogen bonding even in the vapour phase.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 7

Logic Check

Assertion (A): SOCl2 is the preferred reagent for converting carboxylic acids to acyl chlorides. Reason (R): When SOCl2 is used, the by-products are SO2 and HCl, both of which are gases and easily escape, simplifying purification.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 8

Logic Check

Assertion (A): 4-Nitrobenzoic acid is a stronger acid than benzoic acid. Reason (R): The nitro group is electron-withdrawing and destabilises the carboxylate anion of 4-nitrobenzoic acid.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 9

Logic Check

Assertion (A): In aldol condensation, the product formed on dehydration of the beta-hydroxy aldehyde is an alpha,beta-unsaturated carbonyl compound. Reason (R): Loss of water from the beta-hydroxy aldehyde introduces a carbon-carbon double bond conjugated with the carbonyl group.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 10

Logic Check

Assertion (A): The Rosenmund reduction converts acid chlorides to aldehydes. Reason (R): Palladium on BaSO4 is used as a poisoned catalyst to prevent over-reduction of the aldehyde to the corresponding alcohol.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 11

Logic Check

Assertion (A): NaBH4 reduces both carbonyl groups and carboxylic acids. Reason (R): NaBH4 is a mild reducing agent that selectively reduces carbonyl groups of aldehydes and ketones but does not reduce the carboxyl group of carboxylic acids.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 12

Logic Check

Assertion (A): The carbonyl group in aldehydes and ketones makes them polar molecules with higher boiling points than ethers of comparable molecular mass. Reason (R): Aldehydes and ketones can form intermolecular hydrogen bonds with each other, similar to alcohols.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 13

Logic Check

Assertion (A): Electron-withdrawing groups attached to the alpha-carbon of acetic acid increase its acidity. Reason (R): Electron-withdrawing groups stabilise the carboxylate anion by dispersing the negative charge through the inductive effect.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 14

Logic Check

Assertion (A): The iodoform test is used to detect the CH3CO– group or the CH3CH(OH)– group in an organic compound. Reason (R): The iodoform reaction involves oxidation of the CH3– group adjacent to the carbonyl to give CHI3 (yellow precipitate).

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 15

Logic Check

Assertion (A): Aromatic carboxylic acids cannot undergo Friedel-Crafts reactions. Reason (R): The –COOH group is an activating and ortho/para-directing group that facilitates electrophilic substitution.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 16

Logic Check

Assertion (A): Cyanohydrin formation from carbonyl compounds is useful in organic synthesis. Reason (R): Cyanohydrins contain both –CN and –OH groups and can be converted to alpha-hydroxy acids and other useful compounds.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 17

Logic Check

Assertion (A): Addition of NaHSO3 to large ketones is not favoured. Reason (R): Steric hindrance from bulky alkyl groups on the carbonyl carbon in large ketones prevents the sulphite ion from approaching the carbonyl carbon effectively.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 18

Logic Check

Assertion (A): The carbonyl carbon in carboxylic acids is less electrophilic than the carbonyl carbon in aldehydes. Reason (R): In carboxylic acids, the lone pair on the –OH oxygen is delocalised into the carbonyl group through resonance, reducing the positive character of the carbonyl carbon.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 19

Logic Check

Assertion (A): Ketones undergo vigorous oxidation with carbon-carbon bond cleavage to give a mixture of carboxylic acids. Reason (R): Ketones cannot be oxidised by mild oxidising agents because they do not have a hydrogen directly attached to the carbonyl group.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 20

Logic Check

Assertion (A): Diborane (B2H6) is preferred over LiAlH4 for reducing carboxylic acids to primary alcohols when an ester group is also present in the molecule. Reason (R): Diborane does not easily reduce ester groups, allowing selective reduction of the carboxyl group.

Reasoning Options

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Chapter sections

Chapter 8: Aldehydes, Ketones and Carboxylic Acids | Assertion-Reason

Assertion (A): Aldehydes are more reactive than ketones toward nucleophilic addition reactions. Reason (R): In aldehydes, only one alkyl group is attached to the carbonyl carbon, resulting in less steric hindrance and higher electrophilicity of the carbonyl carbon.

Assertion (A): Benzaldehyde does not give a positive Fehling's test. Reason (R): Benzaldehyde lacks an alpha-hydrogen atom.

Assertion (A): Carboxylic acids are stronger acids than phenols. Reason (R): The carboxylate ion has the negative charge delocalised over two equivalent electronegative oxygen atoms, making it more stable than the phenoxide ion.

Assertion (A): Methanal (formaldehyde) is a gas at room temperature. Reason (R): Methanal has a very low molecular mass and lacks significant intermolecular forces.

Assertion (A): The Cannizzaro reaction occurs only with aldehydes that have no alpha-hydrogen. Reason (R): Aldehydes with alpha-hydrogen prefer aldol condensation over disproportionation.

Assertion (A): Carboxylic acids boil at higher temperatures than alcohols of comparable molecular masses. Reason (R): Carboxylic acids exist as dimers through intermolecular hydrogen bonding even in the vapour phase.

Assertion (A): SOCl2 is the preferred reagent for converting carboxylic acids to acyl chlorides. Reason (R): When SOCl2 is used, the by-products are SO2 and HCl, both of which are gases and easily escape, simplifying purification.

Assertion (A): 4-Nitrobenzoic acid is a stronger acid than benzoic acid. Reason (R): The nitro group is electron-withdrawing and destabilises the carboxylate anion of 4-nitrobenzoic acid.

Assertion (A): In aldol condensation, the product formed on dehydration of the beta-hydroxy aldehyde is an alpha,beta-unsaturated carbonyl compound. Reason (R): Loss of water from the beta-hydroxy aldehyde introduces a carbon-carbon double bond conjugated with the carbonyl group.

Assertion (A): The Rosenmund reduction converts acid chlorides to aldehydes. Reason (R): Palladium on BaSO4 is used as a poisoned catalyst to prevent over-reduction of the aldehyde to the corresponding alcohol.

Assertion (A): NaBH4 reduces both carbonyl groups and carboxylic acids. Reason (R): NaBH4 is a mild reducing agent that selectively reduces carbonyl groups of aldehydes and ketones but does not reduce the carboxyl group of carboxylic acids.

Assertion (A): The carbonyl group in aldehydes and ketones makes them polar molecules with higher boiling points than ethers of comparable molecular mass. Reason (R): Aldehydes and ketones can form intermolecular hydrogen bonds with each other, similar to alcohols.

Assertion (A): Electron-withdrawing groups attached to the alpha-carbon of acetic acid increase its acidity. Reason (R): Electron-withdrawing groups stabilise the carboxylate anion by dispersing the negative charge through the inductive effect.

Assertion (A): The iodoform test is used to detect the CH3CO– group or the CH3CH(OH)– group in an organic compound. Reason (R): The iodoform reaction involves oxidation of the CH3– group adjacent to the carbonyl to give CHI3 (yellow precipitate).

Assertion (A): Aromatic carboxylic acids cannot undergo Friedel-Crafts reactions. Reason (R): The –COOH group is an activating and ortho/para-directing group that facilitates electrophilic substitution.

Assertion (A): Cyanohydrin formation from carbonyl compounds is useful in organic synthesis. Reason (R): Cyanohydrins contain both –CN and –OH groups and can be converted to alpha-hydroxy acids and other useful compounds.

Assertion (A): Addition of NaHSO3 to large ketones is not favoured. Reason (R): Steric hindrance from bulky alkyl groups on the carbonyl carbon in large ketones prevents the sulphite ion from approaching the carbonyl carbon effectively.

Assertion (A): The carbonyl carbon in carboxylic acids is less electrophilic than the carbonyl carbon in aldehydes. Reason (R): In carboxylic acids, the lone pair on the –OH oxygen is delocalised into the carbonyl group through resonance, reducing the positive character of the carbonyl carbon.

Assertion (A): Ketones undergo vigorous oxidation with carbon-carbon bond cleavage to give a mixture of carboxylic acids. Reason (R): Ketones cannot be oxidised by mild oxidising agents because they do not have a hydrogen directly attached to the carbonyl group.

Assertion (A): Diborane (B2H6) is preferred over LiAlH4 for reducing carboxylic acids to primary alcohols when an ester group is also present in the molecule. Reason (R): Diborane does not easily reduce ester groups, allowing selective reduction of the carboxyl group.

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