Oxidation-Reduction (redox) reactions take place in the world at every moment. In fact, they are directly related to the origin of life. For instance, oxidation of nutrients forms energy and enables human beings, animals, and plants to thrive. If elements or compounds were exposed to oxygen, after a series of reactions the oxygen will be converted into carbon dioxide or water (combustion). To fully understand redox and combustion reactions, we must first learn about oxidation states (OS).