Answer
$Fe_2(CO_3)_3$
Work Step by Step
Iron(III) has a charge of 3+, as indicated by the "(III)." On the other hand, carbonate has a chemical formula of $(CO_3)_2-$, meaning that it has a charge of 2-. The magnitude of the charge of iron is 1.5 times as great as that of carbonate, meaning that there has to be 1.5 iron atoms for every one carbonate ion. However, we cannot have only half of an atom, so we multiply each side by two in order to create a whole number of atoms. Thus, there are 3 iron (III) ions for every one carbonate ion. This means that the chemical formula for Iron (III) Carbonate is $Fe_2(CO_3)_3$.
