[Free Registration/Login may be required to access all resource tools.] In the following online tutorial students will use the oxidation number rules to determine the oxidation number of an atom of any element in a pure substance. They will define oxidation and reduction in terms of a change in oxidation number and identify which atoms are being oxidized and which atoms are being reduced in a redox reaction. Students will begin to learn which types of reactions are usually redox reactions and which types are usually not and they will use oxidation number changes to decide whether a given reaction involves oxidation and reduction.