What is the chemical formula for oxygen in its free state?

Oxygen, in its free state, refers to the molecular form in which it exists in nature. The correct answer, O2, represents a diatomic molecule of oxygen, meaning it consists of two oxygen atoms bonded together. This is the form of oxygen that is commonly found in the atmosphere and is essential for respiration in most living organisms.

Molecular oxygen (O2) is necessary for processes such as combustion and cellular respiration, both of which rely on this diatomic molecule. It is distinct from other forms mentioned in the choices, such as H2O, which is water and contains both hydrogen and oxygen; or CO2, which is carbon dioxide, comprised of carbon and oxygen. The single oxygen atomic symbol, O, refers to a single atom of oxygen that does not exist independently in nature under normal atmospheric conditions.