First a nit-picking point - oxygen (O2) can be a solid, liquid, or gas depending on temperature and pressure. But I'd guess you probably already know that and are asking why oxygen is a gas at normal earth temperatures and pressures.
In respect to this, is oxygen o2 or just O?
The molecule is O2 because it takes 2 O atoms to make a molecule of oxygen. These types of elements are called diatomic elements, because the element exists in its pure form as a molecule composed of 2 atoms of the element. Oxygen (O2)
Is Oxygen an element or a compound or a mixture?
Oxygen, the element is just a single oxygen atom. Oxygen in real life is O2 and features two oxygen atoms. By that definition it is a compound. Air, the thing we breath is a mixture because it contains nitrogen and oxygen, among other gases.
Is Oxygen is a element?
Element No. 8 on the Periodic Table of the Elements is a colorless gas that makes up 21 percent of Earth's atmosphere. Because it's all around, oxygen is easy to dismiss as dull and inert; in fact, it's the most reactive of the non-metallic elements.