Acid anhydrides on reaction with primary amines give:

The correct answer is Option (1) → An amide

• The reaction is acylation: the amine replaces one hydrogen of its –NH₂ group by an acyl group through nucleophilic substitution. With acetic anhydride and a primary amine:

      \( \displaystyle \ce{R-NH2 + (CH3CO)2O -> R-NH-CO-CH3 + CH3COOH} \)

• The product R–NH–CO–CH₃ (an N-alkylethanamide) is an amide.

Why the other options are incorrect

Option (2) An imide — Incorrect. An imide has two acyl groups on one nitrogen; acylation of the amine puts on one acyl group.

Option (3) A secondary amine — Incorrect. A secondary amine would need an alkyl group on nitrogen; the anhydride brings an acyl (C=O) group, so the product is an amide.

Option (4) An imine — Incorrect. Substituted imines (C=N–R) are formed when amines add to aldehydes and ketones, not to acid anhydrides.

NCERT (2026-27 edition):
9.6 Chemical Reactions – “3. Acylation
Aliphatic and aromatic primary and secondary amines react with acid chlorides, anhydrides and esters by nucleophilic substitution reaction. This reaction is known as acylation. … The products obtained by acylation reaction are known as amides.”