[3] The commercially important dioxides of titanium exists in three distinct structures, for example.In the making of calcium oxide, calcium carbonate (limestone) breaks down upon heating, releasing carbon dioxide:[2] The reaction of elements with oxygen in air is a key step in corrosion relevant to the commercial use of iron especially.For example, zinc powder will burn in air to give zinc oxide:[5] The production of metals from ores often involves the production of oxides by roasting (heating) metal sulfide minerals in air.With a deficiency of oxygen, the monoxide is produced:[2] With excess oxygen, the dioxide is the product, the pathway proceeds by the intermediacy of carbon monoxide: Elemental nitrogen (N2) is difficult to convert to oxides, but the combustion of ammonia gives nitric oxide, which further reacts with oxygen: These reactions are practiced in the production of nitric acid, a commodity chemical.Phosphorus pentoxide is a more complex molecular oxide with a deceptive name, the real formula being P4O10.Many reactions are involved, but the simplified equation is usually shown as:[2] Some metal oxides dissolve in the presence of reducing agents, which can include organic compounds.Reductive dissolution of ferric oxides is integral to geochemical phenomena such as the iron cycle.[11] Because the M-O bonds are typically strong, metal oxides tend to be insoluble in solvents, though they may be attacked by aqueous acids and bases.