Oxygen (O) is a chemical element with atomic number 8. The most abundant oxygen isotope is ¹⁶O, 8 protons and 8 neutrons.

Oxygen is the most abundant element on Earth, and it's the third most abundant in the universe, after hydrogen and helium.

Being part of the water molecule, H₂O, oxygen also makes up most of the mass of living organisms, such as humans.