All these elements belong to sub group IV A. Characteristic of inert pair effect is found in this IV A subgroup elements. Downward elements after Si have less stability by 4 than oxidation state 4 and stability is increased of elements having +2 oxidation state. Where Ge(+4) is stable. In this way Sn(+2) is simple ionic and reducing agent, whereas Sn(+4) is co-ordinator. Half diameter of M2+ is greater than M+4. So, compounds of *** having less valency are more ionic.
