What is the 2 in H_(2) and N_(2) called? superscript subscript Coefficient

The 2 in $H_{2}$ and $N_{2}$ is called a subscript. In chemical formulas, subscripts are used to indicate the number of atoms of the element that are present in the molecule. In this case, the subscript 2 indicates that there are two hydrogen atoms in $H_{2}$ and two nitrogen atoms in $N_{2}$.