How do you turn two positive ions back to atoms?
Give them electrons.
Positive ions are formed when atoms (usually metals) lose electrons. This may be during a reaction, or as a result of electrolysis. To turn the positively charged ions back into atoms we have to find a way of giving them the exact number of electrons they lost. This too might be done by electrolysis, or by reacting them with a substance that could donate the electrons they need.
For example, the copper ions in copper(II) oxide CuO can be turned back into copper atoms by heating the copper(II) oxide in a stream of hydrogen gas. The hydrogen provides the electrons that are needed in this reaction as they form bonds to the oxide ion:
Copper ions gaining electrons (reduction):
Providing the electrons (oxidation):