what is oxygen used for
It is also used to make epoxyethane (ethylene oxide), used as antifreeze and to make polyester, and chloroethene, the precursor to PVC. Oxygen gas is used for oxy-acetylene welding and cutting of metals. A growing use is in the treatment of sewage and of effluent from industry.
Photosynthesis uses energy from the sun to split water into oxygen and hydrogen. The oxygen passes into the atmosphere and the hydrogen joins with carbon dioxide to produce biomass. When living things need energy they take in oxygen for respiration. The oxygen returns to the atmosphere in the form of carbon dioxide. Oxygen gas is fairly soluble in water, which makes aerobic life in rivers, lakes and oceans possible.