Iron bisulfate is a bit of a tricky term because it can refer to two different compounds:

* Iron(II) bisulfate: This is the more common interpretation and has the formula Fe(HSO₄)₂.

* Iron(III) bisulfate: This is less common, but also possible and has the formula Fe(HSO₄)₃.

Here's why this ambiguity exists:

* Iron has two common oxidation states: Fe²⁺ (ferrous) and Fe³⁺ (ferric).

* Bisulfate is the anion: HSO₄⁻, which comes from sulfuric acid (H₂SO₄) losing one proton.

To avoid confusion, it's always best to specify the oxidation state of iron when talking about iron bisulfate.