$ {{({{C}_{2}}{{H}_{5}})}_{2}}\overset{\bullet \,\bullet }{\mathop{N}}\,H $ ( $ 2{}^\circ $ amine) is strongest base. Basic nature of amines due to presences of lone pair of electron on nitrogen atom which is available for the bond formation with Lewis acid. Due to the + $ I $ effect $ 2{}^\circ $ amine is better base than $ 1{}^\circ $ amine and $ N{{H}_{3}} $ . In case of aromatic amines the lone pair on nitrogen atom involved in resonance, therefore, not available for bond formation, so aromatic amines are less basic.