Assertion (A) : Non-metals exhibit variable valency.

Reason (R) : Metals do not exhibit variable valency.

Some non-metals exhibit variable valency .Ex: Sulpher(S) it shows valency 2,4 and 6. Similarly some metals (d-block elements) exhibits variable valencies .In ${\text{FeSO}}_{\text{4}}$valency of iron is 2, but in ${\text{Fe}}_{\text{2}}{{\text{(SO}}_{\text{4}}\text{)}}_{\text{3}}$, valency of iron is 3.