Answer: Oxidation is loss of electrons (rise in positive charge); reduction is gain of electrons (fall in positive charge).
| Oxidation | Reduction |
|---|---|
| Electrons are lost by an atom or ion. | Electrons are gained by an atom or ion. |
| The positive charge increases or the negative charge decreases. | The positive charge decreases or the negative charge increases. |
| Oxygen or a non-metal is added, or hydrogen or a metal is removed, e.g. \(\mathrm{Zn \rightarrow Zn^{2+} + 2e^-}\). | Oxygen is removed, or hydrogen or a metal is added, e.g. \(\mathrm{Cu^{2+} + 2e^- \rightarrow Cu}\). |