What is reduction?
Redox reactions involve the transfer of electrons (
The substance that lost electrons (the substance that was oxidized) is called a reducing agent, while the substance that gained electrons (the substance that was reduced) is called an oxidation agent.
We use oxidation numbers to keep track of the electrons transferred in a redox reaction. The rules for assigning oxidation numbers to each atom belonging to a compound involved in a redox reaction are pretty straightforward, as you can see here
Therefore, a reduction is a chemical reaction in which a compound gains electrons. Here's an example to better illustrate this:
Let's assign oxidation numbers (ON) for every atom (I will not go into the rules for doing this here)
As you can see,
Therefore, the oxygen was reduced by the carbon, while the carbon was oxidized by the oxygen.