Question:
The reagent which does NOT react with both acetone and benzaldehyde is
The reagent which does NOT react with both acetone and benzaldehyde is
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Benedict's and Fehling's reagents oxidise only aliphatic aldehydes, not ketones or aromatic aldehydes.
Updated On: Jul 10, 2026
- Sodium hydrogen sulphite
- Benedict's reagent
- Grignard reagent
- Phenyl hydrazine
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The Correct Option is B
Solution and Explanation
Step 1: We must find the reagent that reacts with neither acetone (a ketone) nor benzaldehyde (an aromatic aldehyde).
Step 2: Benedict's reagent (like Fehling's) is a mild oxidising reagent that oxidises only aliphatic aldehydes. It does not oxidise ketones, so it fails with acetone, and it does not oxidise aromatic aldehydes, so it fails with benzaldehyde. Hence Benedict's reagent reacts with neither compound.
Step 3: Check the others. Sodium hydrogen sulphite (NaHSO3) forms crystalline bisulphite addition compounds with both acetone and benzaldehyde. Grignard reagent adds across the carbonyl (C=O) of both to give alcohols after hydrolysis. Phenyl hydrazine condenses with the carbonyl of both to form phenylhydrazones. So each of these does react with both.
Conclusion: Option (ii) Benedict's reagent is correct.
Step 2: Benedict's reagent (like Fehling's) is a mild oxidising reagent that oxidises only aliphatic aldehydes. It does not oxidise ketones, so it fails with acetone, and it does not oxidise aromatic aldehydes, so it fails with benzaldehyde. Hence Benedict's reagent reacts with neither compound.
Step 3: Check the others. Sodium hydrogen sulphite (NaHSO3) forms crystalline bisulphite addition compounds with both acetone and benzaldehyde. Grignard reagent adds across the carbonyl (C=O) of both to give alcohols after hydrolysis. Phenyl hydrazine condenses with the carbonyl of both to form phenylhydrazones. So each of these does react with both.
Conclusion: Option (ii) Benedict's reagent is correct.
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