Oxidizing agent: An oxidizing agent is an element that gains electrons. Since the oxidizing agent means to gain electrons; it is

said to have been reduced.

The element which undergoes reduction (gets reduced) is called oxidizing agent.

For example: 2Mg + O₂→ 2MgO

In the given reaction, O₂ is reduced by losing oxygen atoms. Thus, O₂ is an oxidizing agent as it undergoes reduction.

Reducing agent: A reducing agent is an element that loses electrons. The reducing agent means to lose electrons; it is said to

have been oxidized.

The element which undergoes oxidation (gets oxidized) is called reducing agent.

For example:

4NH₃ + 5O₂→ 4NO + 6H₂O

In the given reaction, nitrogen is oxidized to NO by gaining oxygen atom. Thus, NH₃ is reducing agent as it undergoes oxidation.