What are oxidation and reduction? Explain a redox reaction using the reaction of copper oxide with hydrogen.

1. 1 · Define in one line. Oxidation is gain of oxygen or loss of hydrogen; reduction is loss of oxygen or gain of hydrogen.
2. 2 · Write the equation. CuO(s) + H₂(g) → Cu(s) + H₂O(l), on heating.
3. 3 · Explain both changes.
   • CuO loses oxygen and becomes Cu: CuO is reduced.
   • H₂ gains oxygen and becomes H₂O: H₂ is oxidised.
4. 4 · Name the reaction. Both happen together, so it is a redox reaction. CuO is the oxidising agent and H₂ is the reducing agent.
5. 5 · Link to real life. Respiration of glucose and the extraction of metals from their oxides are redox reactions.
6. 6 · Close in one line. So in every redox reaction, oxidation and reduction happen at the same time.

Scoring tip: Draw two arrows over the equation, one marked "oxidation" and one marked "reduction". It makes your answer clear at a glance.