oksygen

Oksygen, with the chemical symbol O and atomic number 8, is a colorless, odorless, and tasteless gas at standard conditions. In the atmosphere of Earth it most commonly exists as the diatomic molecule O2, which is highly reactive and supports combustion. Oxygen is the third most abundant element in the universe by mass and the most abundant element by mass in Earth's crust, where it accounts for roughly 46%.

Oxygen occurs widely in minerals as the oxide component of silicates and oxides, and it is a major part of water (H2O). In the atmosphere, a small amount is also present as ozone (O3), formed by photochemical reactions in the upper atmosphere. O3 plays a crucial role in shielding the planet from ultraviolet radiation.

Historically, oxygen was discovered independently by Carl Wilhelm Scheele and Joseph Priestley in 1774. Antoine Lavoisier later named the element and demonstrated its central role in combustion and respiration, helping to refute the phlogiston theory of the time. Oxygen has several allotropes, the most important being O2 and ozone, O3.

Industrial production and supply of oxygen are dominated by cryogenic distillation of air, with supporting methods such as pressure swing adsorption and membrane separation. It is used in steelmaking, chemical synthesis, glass production, and wastewater treatment, and as a medical therapy in concentrated form. As a component of the air we breathe, oxygen sustains aerobic life and features prominently in the Earth’s oxygen cycle, which links photosynthesis, respiration, and oxidation.

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