Step-by-step explanation:
A subscript is defined as a number which is placed slightly below and towards the side of an alphabetical character. A subscript is most commonly used while writing a chemical formula.
For example, chemical formula of calcium chloride is
and here, 2 is the subscript which is placed at the bottom of calcium.
These subscripts represent the number of atoms of an element present in a chemical formula.
Thus, we can conclude that subscripts used in formulas for ionic compounds to represent the number of atoms involved in the chemical reaction.