(i) C to Pb -- The electronic configuration of group 14 elements is ns2 np2. Hence, the most common oxidation state exhibited by them should be +4. On moving down the group, the +2 oxidation state becomes more and more common and the higher oxidation state becomes less stable because of the inert pair effect.Si and c mostly show the +4 state. Although Sn,Ge and Pb shows both the +4 and +2 states, the stability of higher oxidation states decreases than lower oxidation state on moving down the group.
(ii) B to Tl -- Group 13 elements have their electronic configuration of ns2 np1 and the oxidation state exhibited by these elements should be 3. Apart from these two electrons boron and aluminum, other elements of this group exhibit both +1 and +3 oxidation states. Boron and aluminum show oxidation state of +3. This is because of the inert pair effect. The two electrons, which are present in the S-shell do not participate in bonding as they are strongly attracted by the nucleus. As we move down the group, the inert pair effect become more prominent. Therefore Ga (+1) is unstable and TI (+1) is very stable.
On moving down the group, the stability of the +3 oxidation state gets decreased.
