The amine which will not undergo benzoylation in alkaline medium is

N,N-Dimethylaniline

The correct answer is Option (4) → N,N-Dimethylaniline

Benzoylation (reaction with benzoyl chloride) occurs at the –NH₂ group of amines.

• Primary and secondary amines (–NH₂, –NHR) react readily in alkaline medium.
• Tertiary amines (–NR₂) do not undergo benzoylation because they lack a hydrogen on nitrogen.

N,N-Dimethylaniline is a tertiary amine, so it will not undergo benzoylation.