Question

Both transition as well as non-transition elements show variable valencies. Explain.

Answer 1

Variable valency:

On non transition elements: It is due inert pair effect,that on moving down the group,the reluctance of $ns$ orbitals to take part in bond formation.We have variability in order of $2$.

In transition or $d-$orbitals elements:The variability of oxidation states arises out of incomplete filling of $d-$orbitals in such a way that their oxidation state differ by unity .