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The correct order of reactivity towards the electrophilic substitution of the compounds aniline (I), benzene (II) and nitrobenzene (III) is
A
III > II > I
B
II > III > I
C
I III
D
I > II > III
Detailed Solution
The $-NH_2$ group of aniline donates electrons to the ring by resonance (+R effect), increasing the electron density, especially at ortho and para positions. So aniline is much more reactive than benzene towards electrophiles.
The $-NO_2$ group of nitrobenzene withdraws electrons from the ring by both $-I$ and $-R$ effects, decreasing the electron density. So nitrobenzene is much less reactive than benzene.
Order of reactivity: aniline $\gt$ benzene $\gt$ nitrobenzene.
So I $\gt$ II $\gt$ III.
The $-NO_2$ group of nitrobenzene withdraws electrons from the ring by both $-I$ and $-R$ effects, decreasing the electron density. So nitrobenzene is much less reactive than benzene.
Order of reactivity: aniline $\gt$ benzene $\gt$ nitrobenzene.
So I $\gt$ II $\gt$ III.