What is the valency of carbonate ion (${\text{CO}}_3^{2-}$)?

The correct option is A 2
The combining capacity of an element or an ion is known as its valency.

Carbonate ion (${\text{CO}}_3^{2-}$) is an example of a polyatomic ion.

So, valency can be found from the overall charge present on it. Carbonate ion contains two negative charges on it. Therefore, its valency is two.