The correct answer is Only chemical reactions. Explanation & Key Takeaways: • Corrosion can be defined as the process through which refined metals are converted into more stable compounds such as metal oxides, metal sulfides, or metal hydroxides. • The rusting of iron involves the formation of iron oxides via the action of atmospheric moisture and oxygen. • Corrosion is usually an undesirable phenomenon since it negatively affects the desirable properties of the metal. For example, iron is known to have good tensile strength and rigidity (especially when it is alloyed with a few other elements), however, when subjected to rusting, iron objects become brittle, flaky, and structurally unsound. • Corrosion can be classified as an electrochemical process since it usually involves redox reactions between the metal and certain atmospheric agents such as water, oxygen, sulphur dioxide, etc. • If we look at the science behind corrosion then we can say that it is a spontaneous/ irreversible process wherein the metals turn into a much stable chemical compound like oxides, sulphides, hydroxides, etc.