Final answer:
Oxidation is the loss of electrons or gain of oxygen or loss of hydrogen. Reduction is the gain of electrons or loss of oxygen or gain of hydrogen. In redox reactions, oxidation and reduction always occur together.
Step-by-step explanation:
Oxidation and reduction are two processes that occur in chemical reactions called redox reactions. Oxidation can be defined as the loss of electrons or the gain of oxygen or the loss of hydrogen. Reduction, on the other hand, is the opposite of oxidation and involves the gain of electrons or the loss of oxygen or the gain of hydrogen. For example, in the reaction between iron and copper sulfate, iron is oxidized as its oxidation number increases from zero to +2, while copper is reduced as its oxidation number decreases from +2 to 0. Oxidation and reduction always happen together in redox reactions, and they are important in biological systems as well, such as in the process of photosynthesis and digestion of food.