Rust is primarily composed of hydrated iron(III) oxide, also known as ferric oxide, with the chemical formula Fe₂O₃•xH₂O.

Here's a breakdown of the ions involved:

* Iron(III) ion (Fe³⁺): This is the positively charged iron ion present in rust.

* Oxide ion (O²⁻): This is the negatively charged oxygen ion present in rust.

* Hydronium ion (H₃O⁺): This is a positively charged hydrogen ion associated with water molecules in the hydrated form of iron(III) oxide.

While the exact ratio of water molecules (x) in the hydrated formula can vary, the presence of these ions is what defines rust.