What is Oxygen?

Oxygen is a chemical element with the symbol O and atomic number 8. It is a highly reactive nonmetal and an oxidizing agent that readily forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is commonly used for respiration in animals, combustion, and various industrial processes. It's also used in medicine for patients with breathing difficulties, and in welding as it supports a hotter flame than air alone.