O₂ is named oxygen.
Understanding the Chemical Formula O₂
The chemical formula O₂ represents a molecule composed of two oxygen atoms bonded together. This is the most common form of oxygen found in the atmosphere. Because it's a diatomic molecule (two atoms of the same element), the name remains simple: oxygen. We don't need prefixes like "di" to indicate the number of atoms because it's implicitly understood that oxygen gas exists as O₂.
As stated in the provided video reference, "This is a molecular compound and the electrons in that bond between the oxygen [atoms] are shared so to write the name for O₂, this is one you'll see quite a bit in chemistry. We just write oxygen."
