#59)  Since each oxygen atom is -2 and we assume only bound to chromium atoms, we can easily arrive at the correct "empirical" formulas.

If Cr is in the +6 oxidation state, then a neutral substance would have a formula of CrO3.

If Cr is in the +4 oxidation state, then the substance must be CrO2.

Finally, if Cr is in the +3 state, then we need 1.5 oxygen atoms to balance the charge:

OS(Cr) + (n x OS(O)) = 0
+3 + (n x (-2)) = 0
-2n = -3
n = 3/2

This gives us a formula of CrO1.5, but we need to multiply by 2 to get the smallest whole numbers as required for an empirical formula and the substance is Cr2O3.