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Aldehydes, Ketones and Carboxylic Acids: questions with answers

Class 12 Chemistry, Chapter 8 (NCERT). 15 questions by concept. Open “Show answer” for the answer and why.

How to teach this chapter · Common misconceptions & worked visual for this chapter

Carbonyl nomenclature, structure, and physical properties

Question 1

Which statement gives the sound Class XII chemistry for ‘Carbonyl nomenclature, structure, and physical properties’?

  1. (a)The same conclusion about carbonyl nomenclature, structure, and physical properties remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  2. (b)The trigonal-planar polar carbonyl group makes carbon electrophilic. Aldehydes and ketones are named and ranked by substituents, intermolecular forces, and steric/electronic effects; aldehydes are generally more reactive toward nucleophilic addition than comparable ketones.
  3. (c)For carbonyl nomenclature, structure, and physical properties, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  4. (d)Only the name of the substance is needed for carbonyl nomenclature, structure, and physical properties; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
Show answer

(b) The trigonal-planar polar carbonyl group makes carbon electrophilic. Aldehydes and ketones are named and ranked by substituents, intermolecular forces, and steric/electronic effects; aldehydes are generally more reactive toward nucleophilic addition than comparable ketones.

The trigonal-planar polar carbonyl group makes carbon electrophilic. Aldehydes and ketones are named and ranked by substituents, intermolecular forces, and steric/electronic effects; aldehydes are generally more reactive toward nucleophilic addition than comparable ketones.

Question 2

Which principle should be retained when checking an inference about ‘Carbonyl nomenclature, structure, and physical properties’?

  1. (a)The same conclusion about carbonyl nomenclature, structure, and physical properties remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  2. (b)For carbonyl nomenclature, structure, and physical properties, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  3. (c)The trigonal-planar polar carbonyl group makes carbon electrophilic. Aldehydes and ketones are named and ranked by substituents, intermolecular forces, and steric/electronic effects; aldehydes are generally more reactive toward nucleophilic addition than comparable ketones.
  4. (d)Only the name of the substance is needed for carbonyl nomenclature, structure, and physical properties; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
Show answer

(c) The trigonal-planar polar carbonyl group makes carbon electrophilic. Aldehydes and ketones are named and ranked by substituents, intermolecular forces, and steric/electronic effects; aldehydes are generally more reactive toward nucleophilic addition than comparable ketones.

The trigonal-planar polar carbonyl group makes carbon electrophilic. Aldehydes and ketones are named and ranked by substituents, intermolecular forces, and steric/electronic effects; aldehydes are generally more reactive toward nucleophilic addition than comparable ketones.

Question 3

Which statement survives a structure, equation, reagent, and condition audit for carbonyl nomenclature, structure, and physical properties?

  1. (a)For carbonyl nomenclature, structure, and physical properties, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  2. (b)The same conclusion about carbonyl nomenclature, structure, and physical properties remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  3. (c)Only the name of the substance is needed for carbonyl nomenclature, structure, and physical properties; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  4. (d)The trigonal-planar polar carbonyl group makes carbon electrophilic. Aldehydes and ketones are named and ranked by substituents, intermolecular forces, and steric/electronic effects; aldehydes are generally more reactive toward nucleophilic addition than comparable ketones.
Show answer

(d) The trigonal-planar polar carbonyl group makes carbon electrophilic. Aldehydes and ketones are named and ranked by substituents, intermolecular forces, and steric/electronic effects; aldehydes are generally more reactive toward nucleophilic addition than comparable ketones.

The trigonal-planar polar carbonyl group makes carbon electrophilic. Aldehydes and ketones are named and ranked by substituents, intermolecular forces, and steric/electronic effects; aldehydes are generally more reactive toward nucleophilic addition than comparable ketones.

Carboxylic-acid preparation, acidity, and reactions

Question 4

Which statement gives the sound Class XII chemistry for ‘Carboxylic-acid preparation, acidity, and reactions’?

  1. (a)The same conclusion about carboxylic-acid preparation, acidity, and reactions remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  2. (b)Only the name of the substance is needed for carboxylic-acid preparation, acidity, and reactions; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  3. (c)For carboxylic-acid preparation, acidity, and reactions, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  4. (d)Carboxylic acids are stabilised by resonance in the carboxylate ion; electron-withdrawing groups increase acidity. Preparation and reactions include oxidation, nitrile hydrolysis, carbonation of organometallics, esterification, acid-derivative formation, reduction, and decarboxylation under specific conditions.
Show answer

(d) Carboxylic acids are stabilised by resonance in the carboxylate ion; electron-withdrawing groups increase acidity. Preparation and reactions include oxidation, nitrile hydrolysis, carbonation of organometallics, esterification, acid-derivative formation, reduction, and decarboxylation under specific conditions.

Carboxylic acids are stabilised by resonance in the carboxylate ion; electron-withdrawing groups increase acidity. Preparation and reactions include oxidation, nitrile hydrolysis, carbonation of organometallics, esterification, acid-derivative formation, reduction, and decarboxylation under specific conditions.

Question 5

Which principle should be retained when checking an inference about ‘Carboxylic-acid preparation, acidity, and reactions’?

  1. (a)Carboxylic acids are stabilised by resonance in the carboxylate ion; electron-withdrawing groups increase acidity. Preparation and reactions include oxidation, nitrile hydrolysis, carbonation of organometallics, esterification, acid-derivative formation, reduction, and decarboxylation under specific conditions.
  2. (b)Only the name of the substance is needed for carboxylic-acid preparation, acidity, and reactions; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  3. (c)The same conclusion about carboxylic-acid preparation, acidity, and reactions remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  4. (d)For carboxylic-acid preparation, acidity, and reactions, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
Show answer

(a) Carboxylic acids are stabilised by resonance in the carboxylate ion; electron-withdrawing groups increase acidity. Preparation and reactions include oxidation, nitrile hydrolysis, carbonation of organometallics, esterification, acid-derivative formation, reduction, and decarboxylation under specific conditions.

Carboxylic acids are stabilised by resonance in the carboxylate ion; electron-withdrawing groups increase acidity. Preparation and reactions include oxidation, nitrile hydrolysis, carbonation of organometallics, esterification, acid-derivative formation, reduction, and decarboxylation under specific conditions.

Question 6

Which statement survives a structure, equation, reagent, and condition audit for carboxylic-acid preparation, acidity, and reactions?

  1. (a)The same conclusion about carboxylic-acid preparation, acidity, and reactions remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  2. (b)Carboxylic acids are stabilised by resonance in the carboxylate ion; electron-withdrawing groups increase acidity. Preparation and reactions include oxidation, nitrile hydrolysis, carbonation of organometallics, esterification, acid-derivative formation, reduction, and decarboxylation under specific conditions.
  3. (c)Only the name of the substance is needed for carboxylic-acid preparation, acidity, and reactions; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  4. (d)For carboxylic-acid preparation, acidity, and reactions, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
Show answer

(b) Carboxylic acids are stabilised by resonance in the carboxylate ion; electron-withdrawing groups increase acidity. Preparation and reactions include oxidation, nitrile hydrolysis, carbonation of organometallics, esterification, acid-derivative formation, reduction, and decarboxylation under specific conditions.

Carboxylic acids are stabilised by resonance in the carboxylate ion; electron-withdrawing groups increase acidity. Preparation and reactions include oxidation, nitrile hydrolysis, carbonation of organometallics, esterification, acid-derivative formation, reduction, and decarboxylation under specific conditions.

Preparation of aldehydes and ketones

Question 7

Which statement gives the sound Class XII chemistry for ‘Preparation of aldehydes and ketones’?

  1. (a)The same conclusion about preparation of aldehydes and ketones remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  2. (b)Controlled oxidation or dehydrogenation of alcohols, alkene ozonolysis, alkyne hydration, acyl-derivative reduction, and aromatic acylation produce specific carbonyl compounds. Reagent strength and substrate structure stop the reaction from going too far, or decide whether the product is an aldehyde or a ketone.
  3. (c)For preparation of aldehydes and ketones, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  4. (d)Only the name of the substance is needed for preparation of aldehydes and ketones; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
Show answer

(b) Controlled oxidation or dehydrogenation of alcohols, alkene ozonolysis, alkyne hydration, acyl-derivative reduction, and aromatic acylation produce specific carbonyl compounds. Reagent strength and substrate structure stop the reaction from going too far, or decide whether the product is an aldehyde or a ketone.

Controlled oxidation or dehydrogenation of alcohols, alkene ozonolysis, alkyne hydration, acyl-derivative reduction, and aromatic acylation produce specific carbonyl compounds. Reagent strength and substrate structure prevent overreaction or select aldehyde versus ketone.

Question 8

Which principle should be retained when checking an inference about ‘Preparation of aldehydes and ketones’?

  1. (a)Controlled oxidation or dehydrogenation of alcohols, alkene ozonolysis, alkyne hydration, acyl-derivative reduction, and aromatic acylation produce specific carbonyl compounds. Reagent strength and substrate structure stop the reaction from going too far, or decide whether the product is an aldehyde or a ketone.
  2. (b)The same conclusion about preparation of aldehydes and ketones remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  3. (c)Only the name of the substance is needed for preparation of aldehydes and ketones; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  4. (d)For preparation of aldehydes and ketones, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
Show answer

(a) Controlled oxidation or dehydrogenation of alcohols, alkene ozonolysis, alkyne hydration, acyl-derivative reduction, and aromatic acylation produce specific carbonyl compounds. Reagent strength and substrate structure stop the reaction from going too far, or decide whether the product is an aldehyde or a ketone.

Controlled oxidation or dehydrogenation of alcohols, alkene ozonolysis, alkyne hydration, acyl-derivative reduction, and aromatic acylation produce specific carbonyl compounds. Reagent strength and substrate structure prevent overreaction or select aldehyde versus ketone.

Question 9

Which statement correctly governs a new case involving preparation of aldehydes and ketones?

  1. (a)The same conclusion about preparation of aldehydes and ketones remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  2. (b)For preparation of aldehydes and ketones, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  3. (c)Controlled oxidation or dehydrogenation of alcohols, alkene ozonolysis, alkyne hydration, acyl-derivative reduction, and aromatic acylation produce specific carbonyl compounds. Reagent strength and substrate structure stop the reaction from going too far, or decide whether the product is an aldehyde or a ketone.
  4. (d)Only the name of the substance is needed for preparation of aldehydes and ketones; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
Show answer

(c) Controlled oxidation or dehydrogenation of alcohols, alkene ozonolysis, alkyne hydration, acyl-derivative reduction, and aromatic acylation produce specific carbonyl compounds. Reagent strength and substrate structure stop the reaction from going too far, or decide whether the product is an aldehyde or a ketone.

Controlled oxidation or dehydrogenation of alcohols, alkene ozonolysis, alkyne hydration, acyl-derivative reduction, and aromatic acylation produce specific carbonyl compounds. Reagent strength and substrate structure prevent overreaction or select aldehyde versus ketone.

Nucleophilic addition and carbonyl derivatives

Question 10

Which statement gives the sound Class XII chemistry for ‘Nucleophilic addition and carbonyl derivatives’?

  1. (a)Nucleophiles attack the electrophilic carbonyl carbon, followed by proton transfer. Cyanohydrin, bisulfite, acetal, oxime, hydrazone, and Grignard products follow reagent identity; steric and electronic effects control relative reactivity.
  2. (b)The same conclusion about nucleophilic addition and carbonyl derivatives remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  3. (c)Only the name of the substance is needed for nucleophilic addition and carbonyl derivatives; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  4. (d)For nucleophilic addition and carbonyl derivatives, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
Show answer

(a) Nucleophiles attack the electrophilic carbonyl carbon, followed by proton transfer. Cyanohydrin, bisulfite, acetal, oxime, hydrazone, and Grignard products follow reagent identity; steric and electronic effects control relative reactivity.

Nucleophiles attack the electrophilic carbonyl carbon, followed by proton transfer. Cyanohydrin, bisulfite, acetal, oxime, hydrazone, and Grignard products follow reagent identity; steric and electronic effects control relative reactivity.

Question 11

Which principle should be retained when checking an inference about ‘Nucleophilic addition and carbonyl derivatives’?

  1. (a)Only the name of the substance is needed for nucleophilic addition and carbonyl derivatives; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  2. (b)The same conclusion about nucleophilic addition and carbonyl derivatives remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  3. (c)For nucleophilic addition and carbonyl derivatives, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  4. (d)Nucleophiles attack the electrophilic carbonyl carbon, followed by proton transfer. Cyanohydrin, bisulfite, acetal, oxime, hydrazone, and Grignard products follow reagent identity; steric and electronic effects control relative reactivity.
Show answer

(d) Nucleophiles attack the electrophilic carbonyl carbon, followed by proton transfer. Cyanohydrin, bisulfite, acetal, oxime, hydrazone, and Grignard products follow reagent identity; steric and electronic effects control relative reactivity.

Nucleophiles attack the electrophilic carbonyl carbon, followed by proton transfer. Cyanohydrin, bisulfite, acetal, oxime, hydrazone, and Grignard products follow reagent identity; steric and electronic effects control relative reactivity.

Oxidation, reduction, and distinguishing tests

Question 12

Which statement gives the sound Class XII chemistry for ‘Oxidation, reduction, and distinguishing tests’?

  1. (a)Aldehydes oxidise readily to acids and usually respond to Tollens' or Fehling's tests, while ordinary ketones resist mild oxidation. Reduction may give alcohols or methylene groups depending on reagent; test conclusions require the correct structural scope.
  2. (b)Only the name of the substance is needed for oxidation, reduction, and distinguishing tests; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  3. (c)The same conclusion about oxidation, reduction, and distinguishing tests remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  4. (d)For oxidation, reduction, and distinguishing tests, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
Show answer

(a) Aldehydes oxidise readily to acids and usually respond to Tollens' or Fehling's tests, while ordinary ketones resist mild oxidation. Reduction may give alcohols or methylene groups depending on reagent; test conclusions require the correct structural scope.

Aldehydes oxidise readily to acids and usually respond to Tollens' or Fehling's tests, while ordinary ketones resist mild oxidation. Reduction may give alcohols or methylene groups depending on reagent; test conclusions require the correct structural scope.

Question 13

Which principle should be retained when checking an inference about ‘Oxidation, reduction, and distinguishing tests’?

  1. (a)For oxidation, reduction, and distinguishing tests, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  2. (b)Only the name of the substance is needed for oxidation, reduction, and distinguishing tests; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  3. (c)Aldehydes oxidise readily to acids and usually respond to Tollens' or Fehling's tests, while ordinary ketones resist mild oxidation. Reduction may give alcohols or methylene groups depending on reagent; test conclusions require the correct structural scope.
  4. (d)The same conclusion about oxidation, reduction, and distinguishing tests remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
Show answer

(c) Aldehydes oxidise readily to acids and usually respond to Tollens' or Fehling's tests, while ordinary ketones resist mild oxidation. Reduction may give alcohols or methylene groups depending on reagent; test conclusions require the correct structural scope.

Aldehydes oxidise readily to acids and usually respond to Tollens' or Fehling's tests, while ordinary ketones resist mild oxidation. Reduction may give alcohols or methylene groups depending on reagent; test conclusions require the correct structural scope.

Alpha-hydrogen reactions and disproportionation

Question 14

Which statement gives the sound Class XII chemistry for ‘Alpha-hydrogen reactions and disproportionation’?

  1. (a)The same conclusion about alpha-hydrogen reactions and disproportionation remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  2. (b)Only the name of the substance is needed for alpha-hydrogen reactions and disproportionation; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  3. (c)For alpha-hydrogen reactions and disproportionation, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  4. (d)Carbonyl compounds with alpha hydrogen undergo aldol chemistry through enolate formation, whereas aldehydes without alpha hydrogen can undergo Cannizzaro disproportionation in strong base. Haloform reaction requires the methyl-carbonyl pattern or an oxidisable precursor.
Show answer

(d) Carbonyl compounds with alpha hydrogen undergo aldol chemistry through enolate formation, whereas aldehydes without alpha hydrogen can undergo Cannizzaro disproportionation in strong base. Haloform reaction requires the methyl-carbonyl pattern or an oxidisable precursor.

Carbonyl compounds with alpha hydrogen undergo aldol chemistry through enolate formation, whereas aldehydes without alpha hydrogen can undergo Cannizzaro disproportionation in strong base. Haloform reaction requires the methyl-carbonyl pattern or an oxidisable precursor.

Question 15

Which principle should be retained when checking an inference about ‘Alpha-hydrogen reactions and disproportionation’?

  1. (a)The same conclusion about alpha-hydrogen reactions and disproportionation remains valid after changing the reagent, molecular structure, medium, or condition that controls the result.
  2. (b)Only the name of the substance is needed for alpha-hydrogen reactions and disproportionation; equations, structures, stoichiometry, evidence, and conditions cannot change the answer.
  3. (c)For alpha-hydrogen reactions and disproportionation, the relevant direction, trend, product ordering, or cause-and-effect relation is always the exact reverse of the governing rule.
  4. (d)Carbonyl compounds with alpha hydrogen undergo aldol chemistry through enolate formation, whereas aldehydes without alpha hydrogen can undergo Cannizzaro disproportionation in strong base. Haloform reaction requires the methyl-carbonyl pattern or an oxidisable precursor.
Show answer

(d) Carbonyl compounds with alpha hydrogen undergo aldol chemistry through enolate formation, whereas aldehydes without alpha hydrogen can undergo Cannizzaro disproportionation in strong base. Haloform reaction requires the methyl-carbonyl pattern or an oxidisable precursor.

Carbonyl compounds with alpha hydrogen undergo aldol chemistry through enolate formation, whereas aldehydes without alpha hydrogen can undergo Cannizzaro disproportionation in strong base. Haloform reaction requires the methyl-carbonyl pattern or an oxidisable precursor.

Common misconception in Aldehydes, Ketones and Carboxylic Acids

Open full misconception guide →

Will every carbonyl compound give a silver mirror?

Wrong

Both ethanal and propanone give a positive Tollens test because both have C=O.

Why it feels right. I treat all carbonyl groups as having identical chemical behaviour.

Right

Under ordinary Tollens test conditions, an aldehyde such as ethanal can be oxidised. A simple ketone such as propanone does not give the same result.

Worked example

Ethanal
Tollens reagent→Silver mirror can form
Propanone
Same test→No silver mirror
Both contain C=O, but only ethanal gives the silver mirror in this comparison.
  1. Test ethanal and propanone separately.
  2. Ethanal reduces the silver complex and can leave silver on the tube.
  3. Propanone gives no silver mirror in this comparison.