Reduction of nitro compounds

In strongly acidic medium nitrobenzene is reduced to phenylhydroxylamine, which rearranges to p-aminophenol.
$C_6H_5NO_2 \xrightarrow{\text{strongly acidic medium}} C_6H_5NHOH \xrightarrow{\text{rearrangement}} p\text{-}HOC_6H_4NH_2$

The product of reduction of nitrobenzene depends on the medium.
In acidic medium (Sn/HCl or Fe/HCl) nitrobenzene is reduced completely to aniline, $C_6H_5NH_2$.
In neutral medium (Zn dust with aqueous $NH_4Cl$) the reduction stops at the hydroxylamine stage:
In alkaline medium, bimolecular products such as azoxybenzene, azobenzene and hydrazobenzene are formed.
Hence the product with $Zn/NH_4Cl$ is N-phenylhydroxylamine, $C_6H_5NHOH$.