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Schiff's reagent is used to differentiate between which pair of compounds?

1. HCHO and CH3CHO
2. CH3COCH3 and CH3CHO
3. C6H5CH2COCH3 and C6H5COCH2CH3
4. HCHO and C6H5CHO

Correct answer: CH3COCH3 and CH3CHO

Solution

Schiff's reagent gives a pink colour with aldehydes (including HCHO and CH3CHO) but does not react with ketones. So it can distinguish an aldehyde from a ketone: CH3CHO (aldehyde, positive) vs CH3COCH3 (ketone, negative). Options A and D involve two aldehydes — Schiff's cannot differentiate between them (both give pink). Options B is the correct choice.

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