Elemental oxygen, nitrogen, fluorine, and chlorine, IN FACT ALL THE ELEMENTAL GASES EXCEPT FOR the Noble Gases are BIMOLECULAR under standard condtions; i.e. H2, O2, N2, F2, and Cl2. That is the standard elemental state is a diatom, H−H, O=O, N≡N etc............This must simply be known, and the usual problems, even at A level, will ASSUME this knowledge.
Sometimes, we represent sulfur as S8. All of the halogens are X2, but only the two are gases under standard conditions. What about Br2, and I2?
Of course, in compounds, i.e. LiNO3, HClO4, 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.
