Q.The reagent used to distinguish between acetaldehyde and benzaldehyde is a) Tollens' reagent b) Fehling's solution c) 2,4-dinitrophenylhydrazine d) semicarbazide

Step 1. Tollens' reagent (a) and 2,4-DNP (c)/semicarbazide (d) all give a POSITIVE result with BOTH acetaldehyde and benzaldehyde -- Tollens' reagent oxidises essentially any aldehyde (aliphatic or aromatic) to a silver mirror, and 2,4-DNP/semicarbazide simply add to ANY carbonyl compound's electrophilic carbon (Section 12.5.A.4), regardless of whether it is aliphatic or aromatic -- so none of these three can distinguish the two. …

Rule out the three reagents that give the SAME (positive) result for both an aliphatic and an aromatic aldehyde, leaving the one reagent -- Fehling's solution -- whos …

• Picking Tollens' reagent, assuming it is somehow selective -- Tollens' reagent is actually the LEAST selective of the four, oxidising virtually any aldehy …