Oxidation is a chemical reaction that occurs when oxygen combines with another substance, often resulting in the formation of RUST. RUST is a reddish-brown oxide formed when iron or other metals are exposed to oxygen and moisture. Oxidation is a natural process that can cause corrosion and damage to metal objects, such as cars, buildings, and bridges. RUST is an example of oxidation, and it is the result of a chemical reaction between iron and oxygen. RUST can also be caused by other substances, such as salt water, acid rain, and air pollution.