# What is the number placed below an elements symbol in a chemical formula?

Such numbers relate to the $\text{molecularity}$; the molecular composition of the element.........
Elemental oxygen, nitrogen, fluorine, and chlorine, IN FACT ALL THE ELEMENTAL GASES EXCEPT FOR the $\text{Noble Gases}$ are $\text{BIMOLECULAR}$ under standard condtions; i.e. ${H}_{2}$, ${O}_{2}$, ${N}_{2}$, ${F}_{2}$, and $C {l}_{2}$. That is the standard elemental state is a diatom, $H - H$, $O = O$, $N \equiv N$ etc............This must simply be known, and the usual problems, even at A level, will ASSUME this knowledge.
Sometimes, we represent sulfur as ${S}_{8}$. All of the halogens are ${X}_{2}$, but only the two are gases under standard conditions. What about $B {r}_{2}$, and ${I}_{2}$?
Of course, in compounds, i.e. $L i N {O}_{3}$, $H C l {O}_{4}$, the subscript refers to the number of oxygen atoms in a formula unit. Capisce? If this does not address the question you have asked, fire away, and someone will help you.