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Why does iron rust when exposed to water and oxygen?

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A periodic table element box for iron displays its atomic number 26, symbol Fe, atomic weight 55.845, electron configuration, and name. Icons indicate iron is a solid, a transition metal, has a body-centered cubic crystal structure, and equal relative strength. Labels explain each property. — iron Properties of iron.

Iron rusts when exposed to water and oxygen due to a chemical reaction called oxidation. This process transforms iron into iron oxide, commonly known as rust.12

The reaction begins when iron dissolves in moisture, forming ferrous iron and releasing hydrogen. Oxygen then oxidizes the ferrous iron, creating hydrated ferric oxide, which is the reddish-brown rust we see. Water acts as a medium for electron transfer, essential for oxidation, while salts and acids can accelerate the process. Some metals are naturally more resistant to corrosion, and protective measures like coatings can prevent rust.13