Commercial bleaching can be carried out using

Correct answer: chlorine and sulphur(IV) oxide.

Explanation: Commercial bleaching uses agents that remove colour either by oxidation or reduction:

• Chlorine (Cl₂) bleaches by oxidation (in water it forms HOCl), widely used for paper pulp and textiles.
• Sulphur(IV) oxide (SO₂) bleaches by reduction, suitable for delicate materials and some foods.

Why others are wrong:

• Sulphur(IV) oxide and ammonia – Ammonia is not a bleaching agent.
• Hydrogen sulphide and chlorine – H₂S is not used for bleaching; it’s a toxic reducing gas.
• Ammonia and chlorine – This combination is dangerous (forms chloramines), not a bleaching method.