oksigena

Oksigena is the chemical element with the symbol O and the atomic number 8. It is a colorless, odorless gas at room temperature and makes up about 21 percent of the Earth’s atmosphere. Oxygen is essential for most forms of aerobic life and is a key reactant in combustion and many chemical processes.

Historically, oxygen was independently isolated by Carl Wilhelm Scheele and Joseph Priestley in the 1770s, though the element was named by Antoine Lavoisier in 1777. The name derives from Greek roots meaning “acid-former,” a historical misconception that oxygen was a universal component of acids.

In nature, oxygen occurs in several forms. O2, the diatomic molecule, is the most abundant form in the atmosphere and a central element in respiration. O3, or ozone, forms a protective layer in the stratosphere that absorbs ultraviolet radiation. Oxygen is also highly abundant in the Earth's crust (about 46 percent by mass) and in water (as part of H2O, about 89 percent of the mass of water).

Industry and medicine rely on oxygen in various ways. It is produced commercially by fractional distillation of liquid air or by air separation, and also by the electrolysis of water. Major uses include steelmaking, chemical synthesis, medical oxygen therapy, and various processes in electronics and environmental management.

Oxygen has three stable isotopes: O-16, O-17, and O-18, with O-16 by far the most abundant. It is highly reactive, forms oxides with most elements, and supports combustion, which requires careful handling in concentrated environments. Ground-level ozone, while protective in the upper atmosphere, can be harmful to health and materials.