Many elements can have more than one charge or oxidation number. In this set of problems, we will assign oxidation numbers to each atom in sulfate, carbonate, bicarbonate, bisulfate, sulfite, nitrate, nitrite, chlorate, and perchlorate.

Each of the above examples assumes an oxidation number of +1 for hydrogen and -2 for oxygen. There are exceptions to this. We will also look at hydride and peroxide.