- In a redox reaction, compound that is reduced is oxidizing agent. An oxidising agent is substance which oxidises something else.
- Inversely, compound that is oxidised is reducing agent. A reducing agent reduces something else.
- In this reaction, iron(III) oxide is reduced. Therefore it is the oxidising agent. It has oxidised carbon monoxide to become carbon dioxide.
- The carbon monoxide is oxidised. Therefore it act as the reducing agent. It has reduced iron(III) oxide to become iron metal.
- copper(II) oxide is reduced, hence it is the oxidising agent.
- carbon is oxidised, hence it is the reducing agent.