Question

PbCl2 is more stable than PbCl4. Why?

Answer 1

Pb is the element of group 14(the Carbon family); in which the unique property showing variable valency due to INNERT PAIR EFFECT in which the elements from Ge to Pb show the oxidation state +2 and +4. This innert pair effect arises due to the sheilding of s-electrons by intervening d and f-electrons. Hence, as the no. of d and f-electrons increases down the group from Ge to Pb the inert pair effect becomes more prominent and so the +4 o. state becomes less stable. 

So, the + 2 o.s of Pb is more stable therefore PbX2  is more stable than PbX4