Oxygen

Oxygen and its compounds play a key role in many of the important processes of life and industry. Oxygen in the biosphere is essential in the processes of respiration and metabolism, the means by which animals derive the energy needed to sustain life. Furthermore, oxygen is the most abundant element at the surface of the Earth. In combined form it is found in ores, earths, rocks, and gemstones, as well as in all living organisms. …

…are prepared by firing compacted mixtures of iron oxide and one or more metal oxides (such as those of nickel, copper, zinc, magnesium, and manganese). Also of importance in inorganic chemistry are the oxides of the nonmetals. Most of the nonmetals are known to form a wide variety of compounds with oxygen. The nitrogen oxides are undesirable by-products of high-temperature combustion in air (as in an internal combustion engine) and can cause serious environmental pollution.