The formula for iron and nitrate depends on the charge of the iron ion. Iron can have two common charges:

* Iron(II) or Ferrous: Fe²⁺

* Iron(III) or Ferric: Fe³⁺

Here are the formulas for iron and nitrate with each charge:

* Iron(II) nitrate: Fe(NO₃)₂

* Nitrate ion has a charge of -1 (NO₃⁻). To balance the +2 charge of iron(II), two nitrate ions are needed.

* Iron(III) nitrate: Fe(NO₃)₃

* To balance the +3 charge of iron(III), three nitrate ions are needed.