The basicity of a compound in the context of organic bases, such as the aniline derivatives provided, is influenced by the electron-donating or electron-withdrawing nature of substituents attached to the benzene ring. In essence, groups that increase the electron density on the nitrogen atom enhance the compound's basicity because a basic site donates electrons. Conversely, groups that decrease electron density on the nitrogen atom weaken the compound's basicity. [A] p - NO2−C6H4NH2 : The nitro group (NO2) is a strongly electron-withdrawing group via resonance and inductive effects, especially when it is para (p) to the amine (NH2). This significantly decreases the electron density on the nitrogen, making it a weaker base. [B] C6H5−CH2−NH2 : This compound has a benzylamine group, where the amine is not directly attached to the aromatic ring but rather separated by a methylene (CH2) group. This slight separation reduces the direct resonance interaction of the amine with the ring, somewhat preserving the electron density on the nitrogen. Thus, this compound is relatively less affected by the electron-withdrawing effects of the aromatic system. [C] m−NO2−C6H4NH2 : Similar to option [A], the nitro group (NO2) is electron-withdrawing, but it's in the meta (m) position here. While the electron-withdrawing effect is still significant, it's slightly less impactful than in the para position due to the positioning relative to the amine group, affecting basicity through inductive effects rather than resonance. [D] C6H5NH2 : Aniline itself. The lone pair on the nitrogen can participate in resonance with the aromatic ring, slightly decreasing its availability for protonation compared to an aliphatic amine. However, there's no electron withdrawing group directly attached to the ring to decrease its basicity further, making it more basic than the nitro-substituted analogs. Given this understanding, the compound with the highest basicity among the options is [B] C6H5−CH2−NH2 because it's the least affected by the electron-withdrawing effects of an aromatic system, thus preserving more electron density on the nitrogen atom and enabling it to donate electrons more freely. Therefore, the correct answer is: