Question

Oxygen is sometimes represented as O and sometimes as O₂ What is the difference between these symbols?

Answer 1

The first symbol appears to be a typographical zero; it should be the letter $$\mathrm{O}$$, representing one oxygen atom. $$\mathrm{O}_2$$ represents an oxygen molecule containing two chemically bonded oxygen atoms. Thus, the former describes an atom, while the latter describes the usual diatomic form of oxygen.