Final answer:
In order of increasing basicity, aniline (C₆H₅NH₂) is the least basic, followed by water (H₂O), then ammonia (NH₃), and finally methylamine (CH₃NH₂) as the most basic.
Step-by-step explanation:
The question asks to rank the following compounds in order of increasing basicity: NH₃ (ammonia), H₂O (water), CH₃NH₂ (methylamine), and C₆H₅NH₂ (aniline). To evaluate basicity, we consider the tendency of a compound to donate a pair of electrons to a proton (H+). Ammonia is a well-known weak base. Water is amphoteric, acting as a base in the presence of strong acids, but its basicity is weaker than that of ammonia. Methylamine, having an alkyl group, is more basic than ammonia because the alkyl group pushes electron density towards the nitrogen, enhancing its ability to donate electrons. Aniline, however, is less basic than ammonia due to the resonance stabilization of the lone pair on the nitrogen with the benzene ring, making it less available for protonation.
Considering the electronic and structural effects, the compounds can be ranked in order of increasing basicity as follows: C₆H₅NH₂ < H₂O < NH₃ < CH₃NH₂.