Question: why pbcl4 is unstable as compared to pbcl2?
Answer: In case of PbCl4, Pb is in (+4) oxidation state while in PbCl2 it is in (+2) oxidation state. ... When we move down the group, the lower oxidation states become more stable due to the inert pair effect, according to which due to poor shielding of d and f orbitals the valence orbital electrons don't participate in bonding.