Most reactive towards electrophilic substitution is

• In Aniline hydrochloride,

The lone pair of electrons is donated to the hydrogen atom and as result nitrogen has a positive charge on it which decreases the electron density in the compound.

• In Nitrobenzene,

Due to the electron withdrawing nature of the nitro group, the electron density of the ring decreases.

• In N-acetyl aniline,

The lone pair of nitrogen is conjugated with the acetyl group and as a result the overall electron density of the compound decreases.

Thus, aniline has maximum electron density on it.

Electrophilic Substitution reaction Electron density

Therefore, aniline is the most reactive towards electrophilic substitution reaction.