Question

explain ...pbcl4 is less stable than sncl4....but pbcl2 is more stable than sncl2

Answer 1

Due to inert pair effect
Non availability of s electrons for bonding
And it increases down the group. So lead would be more stable in +2 state than +4.
tin shows this effect little less.

Answer 2

As we go down the group, +2 oxidation state becomes more favorable and stable.

Since Pb is more down the group than Sn, it's stable with +2 oxidation state

Sn can exhibit both +2&+4 but +4 is more stable due to which SnCl2 is a strong reducing agent