O−2, also known as oxygen gas, is a diatomic molecule composed of two oxygen atoms. It is essential for the respiration of most living organisms, as it is used to produce energy in cells. O−2 is colorless, odorless, and tasteless, making it undetectable without specialized equipment. In the atmosphere, O−2 constitutes about 21% of the air we breathe. It plays a crucial role in various chemical processes, including combustion and cellular respiration. The presence of O−2 is vital for the survival of many species, including humans, as it supports life on Earth and contributes to the formation of ozone in the stratosphere.