21. Which of the following methods is used to prepare carboxylic acids from nitriles?
a) Hydrolysis
b) Hydrogenation
c) Oxidation
d) Dehydration
Answer: a) Hydrolysis
Explanation: Nitriles are hydrolyzed in acidic or basic conditions to form carboxylic acids. The nitrile group (–CN) is converted into a carboxyl group (–COOH).
22. The reduction of a carboxylic acid to an aldehyde can be accomplished using which reagent?
a) LiAlH₄
b) NaBH₄
c) DIBAL-H (Diisobutylaluminium hydride)
d) H₂/Pd
Answer: c) DIBAL-H (Diisobutylaluminium hydride)
Explanation: DIBAL-H reduces carboxylic acids selectively to aldehydes under controlled conditions, unlike LiAlH₄, which reduces them directly to primary alcohols.
23. Which of the following gives a positive iodoform test?
a) Formaldehyde
b) Acetone
c) Benzaldehyde
d) Propionaldehyde
Answer: b) Acetone
Explanation: The iodoform test is positive for compounds with a methyl ketone group (-COCH₃). Acetone contains this group, so it gives a positive test.
24. Which of the following reactions is used to prepare benzaldehyde from toluene?
a) Friedel-Crafts acylation
b) Clemmensen reduction
c) Etard reaction
d) Cannizzaro reaction
Answer: c) Etard reaction
Explanation: In the Etard reaction, toluene is oxidized to benzaldehyde using chromyl chloride (CrO₂Cl₂).
25. Which reagent will selectively oxidize an aldehyde to a carboxylic acid, leaving a secondary alcohol unchanged?
a) Tollen’s reagent
b) LiAlH₄
c) NaBH₄
d) PCC
Answer: a) Tollen’s reagent
Explanation: Tollen’s reagent oxidizes aldehydes to carboxylic acids but does not affect secondary alcohols, making it selective for aldehydes.
26. Which of the following is the most acidic?
a) Formic acid
b) Acetic acid
c) Trichloroacetic acid
d) Benzoic acid
Answer: c) Trichloroacetic acid
Explanation: Trichloroacetic acid is the most acidic due to the strong electron-withdrawing effect of the three chlorine atoms, which stabilize the negative charge on the conjugate base.
27. Which of the following compounds will undergo nucleophilic addition reactions most readily?
a) Acetone
b) Acetaldehyde
c) Formaldehyde
d) Benzaldehyde
Answer: c) Formaldehyde
Explanation: Formaldehyde is the most reactive towards nucleophilic addition due to the absence of any alkyl or aryl group, which reduces steric hindrance and increases the electrophilicity of the carbonyl carbon.
28. Which of the following carboxylic acids undergoes the fastest esterification reaction with methanol?
a) Formic acid
b) Acetic acid
c) Benzoic acid
d) Propanoic acid
Answer: a) Formic acid
Explanation: Formic acid undergoes the fastest esterification because it has no alkyl or aryl group to provide steric hindrance, and it is more reactive than acetic or benzoic acid.
29. In the reaction of an aldehyde with a Grignard reagent, the product formed is:
a) Primary alcohol
b) Secondary alcohol
c) Tertiary alcohol
d) Ketone
Answer: b) Secondary alcohol
Explanation: The reaction of an aldehyde with a Grignard reagent produces a secondary alcohol after hydrolysis.
30. Which of the following will not react with Fehling’s solution?
a) Glucose
b) Benzaldehyde
c) Formaldehyde
d) Acetaldehyde
Answer: b) Benzaldehyde
Explanation: Benzaldehyde does not react with Fehling’s solution because it is an aromatic aldehyde. Fehling’s solution is typically used to test for aliphatic aldehydes, which are easily oxidized.
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