charges
There are 6 elements in this reaction. All of the monatomic ions have oxidation numbers equal to their charges. Additionally, we can assign an oxidation state of -2 to each oxygen atom and +1 to each hydrogen atom. Now, we just need to assign the oxidation states of manganese in MnO 4 - , nitrogen in the nitrite and nitrate ions, and sulfur in the sulfate ion. These can be determined by choosing a value for which all of the oxidation states in the ion add up to its overall charge. For example, in the nitrite ion.