What is the valency? write the valencies of the calcium, Iron, hydroxyh , Nitrate

(a) : Valency is the measure of the capacity of an atom of a single element to react and combine with particular numbers of atoms of another element.

(b):

Valency of calcium:+2

Valency of Iron:Iron exhibits 2 valence states of + 2 and + 3.

Valency of hydroxl:-1

Valency of Nitrate:-1