Just like the other elements, iron (in a chemical form as Fe), can exist in more than one chemical form. The two most common forms for iron are Fe(II), in which the iron ion shares two of its electrons, and Fe(III), in which it shares three electrons. The roman numerals are used to show the charge of a metal ion when an element can form different charges.
So, the answer for this question is "iron ions with a 2+ charge".
