The +1 oxidation state in group 13 and +2 oxidation state in group 14 becomes more and more stable with increased atomic number. Explain.

Explanation

The outer electronic configuration of group 13 element is `ns^(2) np^(1)` and hence their group oxidation state is `+3`. Both B and Al show an oxidation state of `+3`. Howover , from Ga to Tl. The element have either `d-` or `d-` and f-electrons besides s- and p-electrons . Since d- and f-electrons have poor shielding effect, therefore , they do not screen s-electron of the valence shel effectively from the attraction of the nucleus. Consequently, two s-electrons of the valence shell remain attracted by the nucleus and hence do not participat in bond formation while only the remaining one p-electron of the valence shell participates in bond formation. Further, as the number of d- or d- and f-electron increases down the group, the inert pair effect becomes more nad more prominent. Consequently, the solubility of +3 oxidation state decreases while that of +1 oxidation state increases down the group.
The outer electronic configuation of group 14 element in `ns^(2) np^(2)` and hence their group oxidation state is +4. Both C and Si show an oxidation state of +4. However, from Ge to Pb , the elements have either d- or both d- and f-electrons, in addition to s- and p-electrons. Due to poor shielding of s-electrons of the valence shell by these d- and f-electrons , the inert pair effect comes into play. As a result, the elements from Ge to Pb show oxidation states of +2 and +4 . Further , as the number of d- or d- and f-electrons increases down the group, the inert pair effect becomes more and more perdominant. Consequently, the stability of +4 oxidation state decreases while that of +2 oxidation state increase down the group from Ge to Pb.