Oxygen is a chemical element with the symbol O and atomic number 8. It is a highly reactive gas that makes up approximately 21% of the Earth’s atmosphere by volume. It is also the third-most abundant element in the universe, after hydrogen and helium.

It is essential for life as we know it, as it is required for respiration, which is the process by which living organisms convert food into energy. Oxygen is also used in many industrial processes, including steel production and combustion engines.

It is highly reactive, and it readily combines with other elements to form compounds. Water, for example, is a compound that contains two hydrogen atoms and one oxygen atom (H2O). Oxygen also combines with many metals to form metal oxides.

It has a number of isotopes, including the stable isotopes ^16O, ^17O, and ^18O. The most abundant isotope is ^16O, which makes up approximately 99.76% of natural oxygen. Oxygen can also be produced through nuclear fusion in stars.

Oxygen gas is colorless, odorless, and tasteless. It is slightly soluble in water and is more dense than air. Oxygen gas can be produced through the electrolysis of water or through the fractional distillation of air.

It is used in medicine to treat respiratory disorders and to support patients during surgery. In addition, oxygen therapy is used to treat carbon monoxide poisoning, which can occur when individuals are exposed to high levels of carbon monoxide gas.