Answer:
Hydrogen
Explanation:
Oxidation and reduction are two types of chemical reactions known as redox reactions. (Red - reduction; ox - oxidation).
A substance is oxidized when it receives an oxygen atom from an oxidizing agent. The substance that receives oxygen is known as a reducing agent.
A substance is reduced when it donates an oxygen atom to another atom. Thus, the substance is known as an oxidizing agent - it supplies oxygen.
In the reaction:
CO2(g) + Hz(9) —CO(g) + H2O(1)
CO₂ loses oxygen to become CO and H₂ gains oxygen to become H₂O. Thus, CO₂ is an oxidizing agent and H₂ is a reducing agent.
