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Oxygen is a chemical element with symbol O and atomic number 8. A member of the chalcogen group on the periodic table, it is a highly reactive nonmetal and oxidizing agent that forms oxides with most elements as well as other compounds. By mass, oxygen is the most abundant element in the Earth's crust and the third-most abundant in the universe, after hydrogen and helium. Two atoms of the element can bind to form dioxygen, a colorless and odorless gas that constitutes 20.8% of the Earth's atmosphere, produced by photosynthesis from water and carbon dioxide. Oxygen is present in water, proteins, nucleic acids, carbohydrates, and fats. Its name was coined in 1777 by Antoine Lavoisier, whose experiments helped to discredit the then-popular phlogiston theory of combustion and corrosion. Common uses of oxygen include residential heating, internal combustion engines, production of steel, plastics and textiles, brazing, welding and cutting of steels and other metals, rocket propellant, oxygen therapy, and life support systems in aircraft, submarines, spaceflight and diving. (Full article...)
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