Q.When aniline reacts with acetic anhydride, the product formed is :

Aniline undergoes N-acylation with acetic anhydride: the amine nitrogen's lone pair attacks the anhydride's carbonyl carbon, displacing acetate, to give the amide acetanilide.

Aniline, $C_6H_5NH_2$, has a nucleophilic nitrogen lone pair that attacks the electrophilic carbonyl carbon of acetic anhydride, $(CH_3CO)_2O$, in a nucleophilic acyl substitution reaction. One acetyl group is transferred to nitrogen (displacing acetate/acetic acid as the leaving group), converting the -NH$_2$ into an amide -NHCOCH$_3$ group: $C_6H_5NH_2 + (CH_3CO)_2O \rightarrow C_6H_5NHCOCH_3\ (\text{acetanilide}) + CH_3COOH$ The product, N-phenylacetamide, is commonly called acetanilide, and this specific N-acetylation reaction is also used industrially/in the lab to protect (and mildly deactivate) the -NH$_2$ group before performing further electrophilic aromatic sub …