C6H5NH2 and C6H5NHCH3 are less basic than C2H5NH2 and (C2H5)2NH it is due to the delocalisation of lone pair of electrons of N-atom over the benzene ring. Next, C6H5NHCH3 is little more basic than C6H5NH2 it is due to the +-effect of the CH3 group. Among C2H5NH2 and (C2H5)2NH, (C2H5)2NH is more basic than C2H5NH2 due to greater +l-effect of two C2H5 group. By combining above facts, the relative basic strength of given amines decreases as : (C2H5)2NH>C2H5NH2>C2H5NHCH3>C6H5NH2 As a stronger base has a lower pKb value, therefore, pKb values decreases in the reverse order. (C6H5)NH2>C6H5NHCH3>C2H5NH2 >(C2H5)2NH