Give three examples of elements having variable valency.

Valency:

• The combining capacity of an atom is known as its valency.
• The number of bonds that an atom can form as part of a compound is expressed by the valency of the element.

Variable valency:

• Some metals can lose different numbers of electrons to form ions with different charges, this is called variable valency.
• In some cases, the metals can lose electrons from the inner shell of the atom.
• If an element exhibit two different electropositive valencies, then for lower valency, the suffix -ous is used.
• For higher valency, the suffix -ic is used at the end of the metal name.
• Copper can show two valency ${\mathrm{Cu}}^{+2}\mathrm{and}{\mathrm{Cu}}^{+1}$.
• ${\mathrm{Cu}}^{+2}$ is called Cupric ion and ${\mathrm{Cu}}^{+1}$ is called Cuprous ion.
• Iron $\left(\mathrm{Fe}\right)$ can also show $+2\mathrm{and}+3$ oxidation states.
• Mercury $\left(\mathrm{Hg}\right)$ can show $+1\mathrm{and}+2$ oxidation states.

Hence the transition elements have variable valencies. For example, Copper, Iron, and Mercury.