Oxygen is a colorless, odorless gas that makes up about 21 percent of all breathable air. Oxygen is located in Group 16 of the periodic table of elements, along with sulfur, tellurium, polonium and selenium.
Oxygen is the most abundant element in the Earth's crust. It can be found in water, rocks, minerals and various organic compounds. Oxygen is essential to the respiratory and decay process of most living organisms. It is frequently used in the treatment of medical conditions, such as asthma, hypoxia and carbon monoxide poisoning. Oxygen also has industrial applications, such as smelting, purification of water and oxidation of rocket fuel.