Assertion (A): Aniline can’t be acylated with acetic acid. 

Reason (R): Aniline forms a salt with carboxylic acid.

Aniline can’t be acylated directly with acetic acid because aniline can deprotonate the carboxylic acid to form a highly unreactive carboxylate compound. For this we use glacial acetic acid or acetic anhydride.

Also, direct reaction between aniline and carboxylic acid takes place as,

$\mathrm{Ph}-{\mathrm{NH}}_2+\mathrm{RCOOH}\to \mathrm{Ph}-{\mathrm{NH}}_3{{}^{+}\mathrm{RCOO}}^{-}$

So, Aniline forms a salt with carboxylic acid. Thus, both assertion and reason are true and reason is the correct explanation of assertion

Hence, option (A) is correct.