Out of the following compounds, which is the most basic in aqueous solution?

\((CH_3)_2NH\)

The correct answer is option 2. \((CH_3)_2NH\).

The order of basic strength is \((CH_3)_2NH\) > \(CH_3—NH_2\) > \((CH_3)_3N\) > \(C_6H_5NH_2\)

Aliphatic amines are stronger bases than ammonia because of +I (inductive) effect. The alkyl groups, which are electron-releasing groups, increase the electron density around the nitrogen thereby, increasing the availability of the lone pair of electrons to proton or Lewis acids and making the amine more basic. But in tertiary amines crowding of alkyl groups cover nitrogen atom from all sides and thus makes it unable for protonation. Due to steric factors tertiary amines are less basic than primary amines.