The aldehyde shown gives an orange-yellow crystalline precipitate when it is treated with 2,4-dinitrophenylhydrazine in acid. To which class does the precipitate belong?

AA 2,4-dinitrophenylhydrazone
BA semicarbazone
CA hemiacetal
DAn oxime

Answer: A

Benzaldehyde undergoes addition-elimination (condensation) with 2,4-dinitrophenylhydrazine, losing water. The coloured precipitate is the 2,4-dinitrophenylhydrazone, used as a derivative to identify carbonyl compounds.

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