Nitrobenzene and aniline hydrochloride have electron - withdrawing (−NO2 and−N+H3) ) groups, hence these will undergo electrophilic substitution with difficulty Aniline and N- acetylaniline (acetanilide) have electron- releasing groups, however −NHCOCH3 is less electron- releasing than −NH2 due to delocalisation of lone pair of electron on N toward carbonyl group. Hence aniline (having -NH2) will undergo electrophilic substitution most easily