Explanation

(d)
In the heavier elements of group IIIA, IVA and V A the $ns^{2}$ electrons have extra stability and hence, do not take part in bond formation. The reluctancy of $s$-electron pair to take part in bond formation is known as the inert pair effect. The inert pair effect increases as the atomic number increases in the group.
Lead $(Pb)$ is the element of group 14 (IV A) hence, it shows inert pair effect, hence for lead compounds +2 oxidation state is more predominant.