Question: why pbcl2 is stable than pbcl4?
Answer: due to poor shielding effect of d block and f block ( it means due to poor contraction of d block ) electrons in the s orbital are more strongly held in upper period of same group. So s electrons are inert and can not be removed and give valency of 4. Hence Pb forms 2 ions instead of 4 and PbCl2 becomes stable.