NOTE : Aromatic amines are less basic than aliphatic amines. Among aliphatic amines the order of basicity is 2∘>1∘>3∘. The electron density is decreased in 3∘ 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. ∴ dimethylamine ( 2∘ aliphatic amine) is strongest base among gtiven choices. ∴ The correct order of basic strength is Dimethyl amine > Methyl amine > Trimethyl-amine > Aniline.