Step 1: Understanding the Concept:
Amines are classified by the number of carbon groups attached to the Nitrogen atom: $1^{\circ}$ (one R group), $2^{\circ}$ (two R groups), $3^{\circ}$ (three R groups).
Step 2: Formula Application:
Check the Nitrogen substitution:
- (a) N-methyl...: Two methyls ($2^{\circ}$).
- (c) N-Phenyl...: Two phenyls ($2^{\circ}$).
- (d) N-Ethyl-N-methyl...: Three groups ($3^{\circ}$).
Step 3: Explanation:
4-Bromobenzenamine (also known as $p$-bromoaniline) has only one aryl group attached to the Nitrogen ($Ar-NH_2$). Because the nitrogen is attached to only one carbon atom, it is a primary ($1^{\circ}$) amine.
Step 4: Final Answer:
4-Bromobenzenamine is a primary amine.