Oxygen is essential to humans and other living organisms as it is a chief component of air and water. Oxygen also has many practical industrial applications, such as in health care, medical equipment, fuel burning, water treatment and the melting of certain metals.
Oxygen comprises approximately 21 percent of the air, and it is one of the most abundant elements on earth. Oxygen's practical uses include oxygen therapy for patients, providing fuel for rockets to launch and smelting metal from ore. The chemical symbol for oxygen is O, and its atomic number is eight. Oxygen is a reactive element that forms compounds such as oxides.