Question

since transition metals can have different charges, how do we figure out the charge to write in roman numerals?

Explanation:

Determine the charge by looking at the anion in the compound and using the principle of charge - neutrality. The overall charge of a compound is zero. For example, in iron(III) chloride ($FeCl_3$), chlorine has a - 1 charge and there are 3 chlorine atoms for a total negative charge of - 3. So iron must have a + 3 charge, written as (III) in Roman numerals.

Answer:

Determine the charge based on the anion's charge and charge - neutrality of the compound.