The number written to the right and slightly below a chemical symbol in a chemical formula is called a subscript. It represents the number of atoms of that element present in a molecule or formula unit.

Here are some examples:

* H₂O: This represents a water molecule with two hydrogen atoms (H) and one oxygen atom (O).

* CO₂: This represents a carbon dioxide molecule with one carbon atom (C) and two oxygen atoms (O).

* NaCl: This represents a sodium chloride formula unit (an ionic compound) with one sodium atom (Na) and one chlorine atom (Cl).

Important note: The subscript "1" is usually omitted. For example, "H₂O" is not written as "H₂O₁".