d
Aromatic amines are less basic than aliphatic amines. Among aliphatic amines the order of basicity is \(2^{o}>1^{o}>3^{o} .\) The electron density is decreased in \(3^{o}\) amine due to crowing of alkyl group over \(N\) atom which makes the approach and bonding by a proton relatively difficult. Therefore the basicity decreases. Further Phenyl group show \(- \,I\) effect, thus decreases the electron density on nitrogen atom and hence the basicity.

\(\therefore\)     dimethylamine ( \(2^{o}\) aliphatic amine) is strongest base among gtiven choices.

\(\therefore\)     The correct order of basic strength is Dimethyl amine \(>\) Methyl amine \(>\) Trimethyl-amine \(>\) Aniline.