Williamson's synthesis an example of nucleophilic substitution rxn, in this rxn an alkyl halide is allowed to react with a Na alkokide.

i think the question is wrong.benzene doesn't respond nucleophilic substitution respond electrophilic substitution it is electrophilic then due to resonance there is a partial double bond between carbon of benzene and halogens.so halobenzenes are chemically inert towards electrophilic substitution.

aniline would go through an electrophilic substitution, it is a weak base

Brady's reagent is 2,4-Dinitrophenylhydrazine, its synthesised via aromatic nucleophilic substitution of 1-chloro-2,4-dinitrobenzene and hydrazine (in form of hydrazine sulphate). Its an SN2 reaction i believe. Not too sure about the mechanism yet =\

Aromatic ring present in all dyes structure ,because its mainly based on radical and nucleophilic