What Is the Density of Oxygen Gas at Stp?

These combinations are called oxides. When a molecule of oxygen combines with two molecules of hydrogen, it forms water, which is essential to human life. Oxygen is also part of the air that makes up Earth's atmosphere.

There are two allotropes of oxygen. O2 is a colorless gas, and O3 is ozone, a blue gas with a distinctive, sharp smell. Although ozone is poisonous, Earth's ozone layer protects it from the sun's damaging ultraviolet rays.