Identifying carbonyl compound via chemical tests and empirical formula

Steps:

• Orange precipitate with 2,4-DNPH indicates a carbonyl group (aldehyde or ketone).
• Decolourisation of warm acidified KMnO4 shows the compound is oxidisable, consistent with an aldehyde.
• Empirical formula C2H4O has one degree of unsaturation, matching a simple aldehyde like ethanal (CH3CHO).
• Ethanal fits both tests: forms hydrazone with DNPH and oxidises to ethanoic acid with KMnO4.

Why A is correct:

• A is ethanal (CH3CHO), an aldehyde that reacts with DNPH to form an orange precipitate and reduces KMnO4 due to its aldehydic hydrogen.

Why the others are wrong:

• B (oxirane) lacks a carbonyl, so no DNPH reaction.
• C (ethenol) is unstable and tautomerises to ethanal, not a distinct compound.
• D (ethanal hydrate) has formula C2H6O2, not matching C2H4O.

Final answer: A