Concept:Rusting is a corrosion process in which iron reacts with oxygen and water.
Explanation:When iron is exposed to moist air, oxygen from the air and water both take part in the reaction.
This oxidation reaction produces hydrated iron(III) oxide, which is the reddish-brown substance known as rust.
Rust is not anhydrous iron(III) oxide, because it contains water of crystallisation in its structure.
A simplified equation for the process is:
4Fe(s)+3O2(g)+xH2O(l)→2Fe2O3⋅xH2O(s)The iron is oxidised to the
+3 oxidation state, forming hydrated iron(III) oxide.
Answer:A. hydrate iron (III) oxide.