Explanation

[Solution from source] In benzylamine, C₆H₅CH₂NH₂, the CH₂ group separates nitrogen from the ring, so its lone pair is not delocalised and it behaves like an alkylamine, more basic than aniline. In diphenylamine and triphenylamine the lone pair is spread over two or three rings, and the nitro group in p-nitroaniline withdraws electrons, so all three are weaker than aniline. Answer (4).