Step 1: Rank basicity by how much the nitrogen lone pair is tied up by resonance or pulled by electron-withdrawing groups; a tied-up or pulled lone pair means weaker base.
Step 2: In aniline the lone pair spreads into the aromatic ring, lowering basicity relative to a plain alkyl amine. Adding a \( -NO_2 \) group (p-nitroaniline) drains electron density further, and turning the amine into an amide (acetanilide) locks the lone pair onto the carbonyl oxygen, the strongest deactivation of all.
Step 3: Benzyl amine keeps its nitrogen one carbon away from the ring. That insulating \( CH_2 \) blocks resonance with the ring, so its lone pair is as available as in an ordinary aliphatic amine.
Step 4: With the freest lone pair, benzyl amine accepts a proton most readily and is therefore the most basic of the four. Option (iii) is correct.