Among the following identify the elements which show a variable valency?

Cu, Zn, Co, Fe, Sn, Pb, Ba, and Al.

• Variable valency is the change in valency of the element according to condition.
• There are some elements that can combine with other atoms, either by electron exchange or sharing of electrons in different proportions, with each type of reaction, these elements exhibit variable valency.
• The variable valency is shown by certain elements due to their unique electronic configuration. The atom of such an element can lose electrons from its penultimate shell in addition to the outermost valency shell and so, can exhibit variable valency.
• Some chemical elements show more than one valency or variable valency.
• Cu has two different valencies i.e Cu⁺¹ (Cuprous)and Cu⁺²(Cupric)
• Fe has two valencies Fe²⁺ (Ferrous), Fe³⁺(Ferric).
• Sn has two valencies Sn⁺²(Stannous), Sn⁺⁴(Stannic).
• Pb has two valencies Pb²⁺(Plumbous), Pb⁴⁺(Plumbic)
• The most common oxidation states of Cobalt are +2 and +3
• Zn, Ba, and Al all have single valency (+2, +2, +3 respectively).

Therefore, Cu, Co,Fe, Sn,Pb have variable valencies.