Explain inert pair effect with reference to carbon family.
Or
Explain C and Si are tetravalent, but Ge, Sn and Pb show divalent.

The general electronic configuration of group 14 elements is [Noble gas] ns²np², so these elements are expected to show a uniform oxidation state of +4. Carbon and silicon show an oxidation state of +4 only, but tin and lead, however, show oxidation states of +2 and +4.
As we move down the group, the stability of +4 oxidation state decreases and that of+2 oxidation state increases. This means that as we move down the group, the tendency of the s- electron of the valence shell to precipitate in a bond formation decreases. In other words, the pair of s-electrons, 5s in tin and 6s in lead behaves as inert. This is called inert pair effect. Because of inert pair effect, only the np² electron of tin and lead take part in bonding with the atoms of the other elements. Thus, divalent compounds of tin and lead are stable.