Aniline is a very strongly activating substrate because its nitrogen lone pair donates electron density into the ring, which makes direct nitration difficult to control and prone to oxidation and excessive ortho substitution. Acetylation with acetic anhydride converts the –NH2 group into an acetamido group –NHCOCH3, in which the nitrogen lone pair is partly delocalised onto the acetyl carbonyl. This tempers the ring's reactivity, protects nitrogen from oxidation by the nitrating mixture, and increases the proportion of the para product by steric and electronic control. After nitration, hydrolysis regenerates the free amino group. The option about increasing basicity is wrong; acetylation lowers basicity by withdrawing the lone pair. It does not create a tertiary amine, since the nitrogen still bears a hydrogen and an acyl group, forming an amide, not a tertiary amine. Volatility for distillation is irrelevant to the synthetic purpose. This protective acetylation strategy is the standard NCERT explanation for controlled aromatic substitution on aniline, and the acetyl group is removed by acid or base hydrolysis once substitution is complete. As a plausibility check, the higher para selectivity and the absence of oxidative tar confirm that moderating reactivity is the achieved objective, while the recovery of the free amine after hydrolysis confirms the group acted only as a temporary protector.