Calculate the oxidation number of the chlorine in perchloric acid, hclo4, a strong oxidizing agent.

The oxidation number that is given to chlorine in a chemical combination indicates how many electrons are gained or lost because it is a neutral compound, perchloric acid has a total charge of 0. Hydrogen has an oxidation number of + 1, whereas oxygen has an oxidation number of - 2. So for the total charge to be 0, 1 hydrogen + 4 oxygen of negative charge added together must equal 0, which will make the oxidation number of chlorine, solving this algebraically + 7.