The correct option is D Aniline
The benzene ring with the maximum electron density reacts with the fastest rate.
Due to the −R effect of NH2 in aniline, it is more reactive than benzene. Due to electron withdrawing nature of −COOH group in benzoic acid and −NO2 group in nitrobenzene, both benzoic acid and nitrobenzene are less reactive than benzene.
Hence, the correct option is (d).