Which one is weakest base among these?

Explanation

Aniline is the weakest base among the options because the nitrogen's lone pair of electrons is delocalized into the benzene ring, making it less available for protonation. In contrast, pyridine, ammonia, and methylamine have nitrogen atoms with lone pairs that are more available for bonding with protons. Pyridine's nitrogen is part of an aromatic heterocycle, but its lone pair is not involved in resonance, making it more basic than aniline. Ammonia has a straightforward structure with an available lone pair, and methylamine's nitrogen is further activated by the electron-donating effect of the methyl group, making them both stronger bases.