Question

Why is +2 oxidation state of pb more stable than +4 oxidation state?

Answer 1

Any Ion is more stable with less charge. That's why Pb ion of 2+ charge is more stable with 2 more electrons than that of Pb 4+ ion.

Answer 2

In carbon family,lead is the element which is the most affected due to this( Pb2+ is more stable than Pb4+). And for this reason,Sn4+ is slightly more stable than Sn2+ though tin does form compounds in both the oxidation states.