What is the chemical name for rust?

Rust is primarily known as hydrated iron(III) oxide, specifically represented as Fe₂O₃·nH₂O, where 'n' indicates that water is incorporated in the form of hydration. This compound forms through the oxidation of iron in the presence of water and oxygen, resulting in a complex mixture typically associated with the corrosion process of iron and its alloys.

The presence of water in the formula highlights the hydrated aspect of rust, distinguishing it from simple iron oxides that do not include water in their composition. Other choices refer to different forms of iron oxides; for instance, Iron(II) oxide consists of iron in a +2 oxidation state, while Iron(III) oxide is a dehydrated form without water. Iron oxide, while it might seem a general term for iron oxides, does not specify the hydrated nature that is characteristic of rust. Thus, specifying it as hydrated iron(III) oxide accurately captures both the composition and the conditions under which rust forms.