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Fe2O3. XH2O
Fe2O3.XH2O

Several forms of rust are distinguishable visually and by spectroscopy, and form under different circumstances.Rust consists of hydrated iron(III) oxides\xa0Fe2O3.nH2O, iron(III) oxide-hydroxide (FeO(OH), Fe(OH)3. Rusting is the common term for corrosion of iron and its alloys, such as steel.

The chemical equation for the formation of rust is:Iron + Water + Oxygen = Rusti.e. 4 Fe(s) + 6 H2O(l) + 3 O2(g) → 4 Fe(OH)3(s)Then Fe(OH)3 dehydrates to produce Fe2O3.nH2O(s).Thereby, the chemical formula for rust is Fe2O3.nH2O.