Answer:
+6 per Cr molecule, +12 overall.
Explanation:
Refer to a oxidation table, where O usually has an oxidation # of -2 (unless it's H2O2, where it's -1). We have 7 molecules of Oxygen, so we have a total of -14 on Oxygen. We also know group 1 metals all have an oxidation # of +1 so we can say potassium (K) has an oxidation # of +1 per molecule, +2 overall.
Before we determine Cr let's check what the overall charge is, in this compound its 0 (neutral), so we just Cr to help K balance out the -14 charge on Oxygen. We can look at like this.
14= x +2
Where x is Chromium.
14 -2 = 12
So Chromium will have a +12 charge but we have 2 molecules, so each Chromium will have a +6 charge.
