Question

What is variable valency ? Give two examples of elements showing variable valency.

Answer 1

Certain elements exhibit more than one valency, that means they show variable valency.
Ferrous is written as Iron (II) and Ferric is written as Iron (III).
Metal Radicals Valency
Iron:

Ferrous [Iron (II)] = $F{e}^{+2}$
Ferric [Iron (III)] = $F{e}^{+3}$

Copper
Cuprous [Copper (Il)] = $C{u}^{+2}$
Cupric [Copper (I)]= $C{u}^{+}$