O2

Definition

O2 or Oxygen gas is a colorless, odorless reactive gas that forms about 21% of the earth's atmosphere. It supports combustion and respiration in most living organisms.

Related terms

Oxidation: A chemical reaction that involves the loss of electrons or an increase in oxidation state by a molecule, atom, or ion.

Respiration: The metabolic process where organisms inhale oxygen from their environment to produce energy from food molecules.

Ozone (O3): An allotrope of oxygen that consists of three oxygen atoms bonded together.