MCQs on Aldehydes, Ketones and Carboxylic Acids – Class 12
MCQs on Aldehydes, Ketones and Carboxylic Acids – CBSE Class 12 Chemistry
Organic Chemistry | NCERT-Based | MCQs with Answers & Explanations
The following 50 Multiple Choice Questions (MCQs) are strictly based on the NCERT syllabus for CBSE Class 12 Chemistry.
They are arranged section-wise to comprehensively cover aldehydes, ketones, and carboxylic acids, including structure, nomenclature, preparation, physical properties, chemical reactions, and tests, with concept-clearing explanations ideal for CBSE board exam preparation.
Section A: Aldehydes – Structure, Properties & Preparation
Q1. Aldehydes contain which functional group?
A. –COOH
B. –CO–
C. –CHO
D. –OH
Answer: C
Explanation:
Aldehydes contain the –CHO (formyl) group, where carbonyl carbon is bonded to one hydrogen atom.
Q2. Which of the following is an aldehyde?
A. CH₃COCH₃
B. CH₃CHO
C. CH₃COOH
D. C₆H₅COCH₃
Answer: B
Explanation:
CH₃CHO (ethanal) contains the –CHO group, characteristic of aldehydes.
Q3. Aldehydes are generally prepared by oxidation of:
A. Tertiary alcohols
B. Secondary alcohols
C. Primary alcohols
D. Phenols
Answer: C
Explanation:
Controlled oxidation of primary alcohols yields aldehydes.
Q4. Which reagent is used to oxidize primary alcohols to aldehydes without further oxidation?
A. KMnO₄
B. K₂Cr₂O₇
C. PCC
D. HNO₃
Answer: C
Explanation:
PCC (pyridinium chlorochromate) oxidizes alcohols to aldehydes without forming acids.
Q5. Which aldehyde is also called formaldehyde?
A. Methanal
B. Ethanal
C. Propanal
D. Benzaldehyde
Answer: A
Explanation:
Methanal (HCHO) is commonly known as formaldehyde.
Section B: Chemical Reactions of Aldehydes
Q6. Aldehydes are easily oxidized to:
A. Alcohols
B. Ketones
C. Carboxylic acids
D. Esters
Answer: C
Explanation:
Aldehydes readily oxidize to carboxylic acids.
Q7. Which test is used to distinguish aldehydes from ketones?
A. Lucas test
B. Tollens’ test
C. Victor Meyer test
D. Iodoform test
Answer: B
Explanation:
Aldehydes give silver mirror with Tollens’ reagent, ketones do not.
Q8. Fehling’s solution gives positive test with:
A. All aldehydes
B. Aromatic aldehydes
C. Aliphatic aldehydes
D. Ketones
Answer: C
Explanation:
Only aliphatic aldehydes reduce Fehling’s solution.
Q9. Benzaldehyde does not give Fehling’s test because:
A. It is insoluble
B. It is aromatic
C. It is highly stable
D. It is acidic
Answer: B
Explanation:
Aromatic aldehydes do not reduce Fehling’s solution.
Q10. Aldehydes react with alcohols in presence of acid to form:
A. Esters
B. Ethers
C. Acetals
D. Ketals
Answer: C
Explanation:
Aldehydes form acetals on reaction with alcohols.
Section C: Ketones – Structure, Properties & Preparation
Q11. Ketones contain which functional group?
A. –CHO
B. –COOH
C. –CO–
D. –OH
Answer: C
Explanation:
Ketones contain a carbonyl group (–CO–) bonded to two carbon atoms.
Q12. Which compound is a ketone?
A. CH₃CHO
B. CH₃COCH₃
C. HCHO
D. HCOOH
Answer: B
Explanation:
CH₃COCH₃ (propanone) is a ketone.
Q13. Ketones are generally prepared by oxidation of:
A. Primary alcohols
B. Secondary alcohols
C. Tertiary alcohols
D. Aldehydes
Answer: B
Explanation:
Oxidation of secondary alcohols produces ketones.
Q14. Which ketone is commonly known as acetone?
A. Methanone
B. Ethanone
C. Propanone
D. Butanone
Answer: C
Explanation:
Propanone (CH₃COCH₃) is commonly called acetone.
Q15. Ketones do not undergo oxidation easily because:
A. They lack hydrogen
B. They lack α-hydrogen
C. They lack hydrogen attached to carbonyl carbon
D. They are aromatic
Answer: C
Explanation:
Ketones lack hydrogen on the carbonyl carbon, making oxidation difficult.
Section D: Chemical Reactions of Ketones
Q16. Which reagent reduces ketones to secondary alcohols?
A. KMnO₄
B. NaBH₄
C. Tollens’ reagent
D. Fehling’s solution
Answer: B
Explanation:
NaBH₄ reduces ketones to secondary alcohols.
Q17. Which test is common to both aldehydes and ketones?
A. Tollens’ test
B. Fehling’s test
C. Iodoform test
D. Lucas test
Answer: C
Explanation:
Iodoform test is given by compounds containing –COCH₃ group.
Q18. Which ketone gives positive iodoform test?
A. Propanone
B. Butanone
C. Both A and B
D. None
Answer: C
Explanation:
Both contain the methyl ketone group.
Q19. Ketones react with Grignard reagent to form:
A. Primary alcohols
B. Secondary alcohols
C. Tertiary alcohols
D. Acids
Answer: C
Explanation:
Ketones form tertiary alcohols with Grignard reagents.
Q20. Ketones react with hydroxylamine to form:
A. Oximes
B. Hydrazones
C. Semicarbazones
D. Esters
Answer: A
Explanation:
Reaction with hydroxylamine forms oximes.
Section E: Carboxylic Acids – Structure & Properties
Q21. Carboxylic acids contain which functional group?
A. –CHO
B. –CO–
C. –COOH
D. –OH
Answer: C
Explanation:
Carboxylic acids contain the –COOH (carboxyl) group.
Q22. Which compound is a carboxylic acid?
A. CH₃CHO
B. CH₃COCH₃
C. CH₃COOH
D. CH₃OH
Answer: C
Explanation:
CH₃COOH is ethanoic acid, a carboxylic acid.
Q23. Carboxylic acids are more acidic than alcohols because:
A. Presence of oxygen
B. Hydrogen bonding
C. Resonance stabilization of carboxylate ion
D. High molecular mass
Answer: C
Explanation:
Carboxylate ion is resonance-stabilized, increasing acidity.
Q24. Which acid is called vinegar?
A. Formic acid
B. Oxalic acid
C. Acetic acid
D. Benzoic acid
Answer: C
Explanation:
Acetic acid (ethanoic acid) is present in vinegar.
Q25. Carboxylic acids exist as dimers due to:
A. Covalent bonding
B. Ionic bonding
C. Hydrogen bonding
D. Van der Waals forces
Answer: C
Explanation:
Strong intermolecular hydrogen bonding causes dimer formation.
Section F: Preparation & Reactions of Carboxylic Acids
Q26. Carboxylic acids can be prepared by oxidation of:
A. Ketones
B. Aldehydes
C. Alkenes
D. Alkynes
Answer: B
Explanation:
Aldehydes oxidize easily to carboxylic acids.
Q27. Which reagent converts nitriles into carboxylic acids?
A. NaOH
B. H₂O
C. Acidic hydrolysis
D. NaBH₄
Answer: C
Explanation:
Hydrolysis of nitriles gives carboxylic acids.
Q28. Carboxylic acids react with alcohols to form:
A. Ethers
B. Aldehydes
C. Esters
D. Ketones
Answer: C
Explanation:
This reaction is known as esterification.
Q29. Which gas is released when carboxylic acid reacts with NaHCO₃?
A. H₂
B. O₂
C. CO₂
D. N₂
Answer: C
Explanation:
CO₂ evolution confirms the presence of –COOH group.
Q30. Which acid is the strongest among the following?
A. Acetic acid
B. Formic acid
C. Propionic acid
D. Butyric acid
Answer: B
Explanation:
Formic acid has no electron-donating alkyl group, so it is most acidic.
Section G: NCERT-Based Mixed MCQs
Q31. Which compound reduces Tollens’ reagent?
A. Propanone
B. Benzophenone
C. Ethanal
D. Acetone
Answer: C
Explanation:
Ethanal is an aldehyde and reduces Tollens’ reagent.
Q32. Which compound gives both Fehling’s and Tollens’ test?
A. Benzaldehyde
B. Formaldehyde
C. Acetone
D. Benzophenone
Answer: B
Explanation:
Formaldehyde is an aliphatic aldehyde.
Q33. Which compound cannot show optical isomerism?
A. Butanal
B. Propanone
C. 2-Hydroxypropanoic acid
D. Lactic acid
Answer: B
Explanation:
Propanone has no chiral carbon.
Q34. Which functional group gives nucleophilic addition reactions?
A. –COOH
B. –CHO and –CO–
C. –OH
D. –NH₂
Answer: B
Explanation:
Carbonyl group undergoes nucleophilic addition.
Q35. Which compound gives iodoform test?
A. Ethanal
B. Methanal
C. Benzaldehyde
D. Formic acid
Answer: A
Explanation:
Ethanal contains –COCH₃ equivalent structure.
Q36. Which acid is used as food preservative?
A. Oxalic acid
B. Benzoic acid
C. Formic acid
D. Citric acid
Answer: B
Explanation:
Benzoic acid prevents microbial growth.
Q37. Which compound reacts with Na metal to release H₂ gas?
A. Ketone
B. Aldehyde
C. Carboxylic acid
D. Ester
Answer: C
Explanation:
Acidic hydrogen of –COOH reacts with sodium.
Q38. The boiling point of carboxylic acids is high due to:
A. Large size
B. Ionic nature
C. Hydrogen-bonded dimers
D. Polarity only
Answer: C
Explanation:
Dimer formation via hydrogen bonding raises boiling point.
Q39. Which compound undergoes Cannizzaro reaction?
A. Ethanal
B. Acetone
C. Formaldehyde
D. Propanal
Answer: C
Explanation:
Aldehydes without α-hydrogen undergo Cannizzaro reaction.
Q40. Which compound gives fruity smell?
A. Aldehydes
B. Ketones
C. Esters
D. Acids
Answer: C
Explanation:
Esters generally have pleasant fruity odors.
Q41. Which reagent oxidizes aldehydes but not ketones?
A. KMnO₄
B. Tollens’ reagent
C. NaBH₄
D. H₂/Ni
Answer: B
Explanation:
Tollens’ reagent selectively oxidizes aldehydes.
Q42. Which acid shows strongest intermolecular hydrogen bonding?
A. Formic acid
B. Acetic acid
C. Benzoic acid
D. Oxalic acid
Answer: A
Explanation:
Formic acid forms strong hydrogen bonds due to small size.
Q43. Which compound does not undergo nucleophilic addition?
A. Aldehyde
B. Ketone
C. Carboxylic acid
D. Formaldehyde
Answer: C
Explanation:
Carboxylic acids undergo nucleophilic substitution, not addition.
Q44. Which aldehyde is aromatic?
A. Ethanal
B. Propanal
C. Benzaldehyde
D. Methanal
Answer: C
Explanation:
Benzaldehyde contains an aromatic ring.
Q45. Which compound shows keto–enol tautomerism?
A. Methanal
B. Ethanal
C. Acetic acid
D. Formaldehyde
Answer: B
Explanation:
Ethanal has α-hydrogen, enabling tautomerism.
Q46. Which acid is dibasic?
A. Acetic acid
B. Formic acid
C. Oxalic acid
D. Benzoic acid
Answer: C
Explanation:
Oxalic acid contains two –COOH groups.
Q47. Which compound forms cyanohydrin?
A. Aldehyde
B. Ketone
C. Both A and B
D. Carboxylic acid
Answer: C
Explanation:
Both aldehydes and ketones form cyanohydrins.
Q48. Which compound gives white precipitate with NaHCO₃?
A. Ethanol
B. Phenol
C. Acetic acid
D. Aldehyde
Answer: C
Explanation:
CO₂ evolution confirms carboxylic acid.
Q49. Which compound is reduced to secondary alcohol?
A. Aldehyde
B. Ketone
C. Acid
D. Ester
Answer: B
Explanation:
Reduction of ketone gives secondary alcohol.
Q50. Which functional group is present in aspirin?
A. Aldehyde
B. Ketone
C. Carboxylic acid
D. Ether
Answer: C
Explanation:
Aspirin contains a carboxylic acid group.
✅ CBSE Exam Tip:
These MCQs are 100% NCERT-aligned, concept-rich, and ideal for Class 12 board exams, revision practice, and objective assessments.