Aniline reacts through its ring or its nitrogen depending on the reagent; here is what each does.
i) Bromine water: Because the lone pair on nitrogen feeds electron density into the ring, aniline is far more reactive than benzene toward electrophiles. Bromine water needs no iron catalyst and puts three bromines on the ring in one go, at the two ortho spots and the para spot. The insoluble white solid formed is 2,4,6-tribromoaniline, and \(3HBr\) is released.
ii) Acetic anhydride with pyridine: Here the nitrogen, not the ring, reacts. The lone pair of \(-NH_2\) attacks the anhydride and an acetyl group (\(CH_3CO-\)) is stitched onto nitrogen, converting the amine into an amide. The product is acetanilide, \(C_6H_5NHCOCH_3\). Pyridine mops up the acetic acid side product, so the reaction runs cleanly. (This step is also used to protect the amino group before further ring reactions.)
iii) Nitrous acid with HCl at 0-5 °C: Cold nitrous acid, made in situ from \(NaNO_2 + HCl\), converts the \(-NH_2\) into a diazonium group. The chilly temperature keeps the fragile salt from decomposing. The product is benzenediazonium chloride, \(C_6H_5N_2^{+}Cl^{-}\), along with water. This salt is a key starting point for making many substituted benzenes.
\(\boxed{i)\ 2,4,6\text{-tribromoaniline};\ ii)\ \text{acetanilide};\ iii)\ \text{benzenediazonium chloride}}\)