Commercial bleaching can be carried out using

Analyze the question: It asks which pair of substances is used for commercial bleaching.

Concept: Bleaching agents work in one of two ways:

• Chlorine (Cl₂) bleaches by oxidation. In water it forms hypochlorous acid, which releases nascent oxygen: Cl₂ + H₂O → HCl + HOCl HOCl → HCl + [O] The [O] oxidises coloured substances into colourless ones. Moist chlorine is therefore a good bleach, especially for cotton, paper pulp and linen.
• Sulphur (IV) oxide (SO₂) bleaches by reduction. In water it gives sulphurous acid, which takes oxygen from the dye or adds hydrogen: SO₂ + H₂O → H₂SO₃ It is used for bleaching wool, silk, straw and paper.

Checking the options:

• A. SO₂ is a bleach, but ammonia is not. ✗
• B. H₂S is a reducing agent and not a commercial bleach, though chlorine is a bleach. ✗
• C. Chlorine and SO₂ are both bleaching agents. ✓
• D. Chlorine is a bleach, but ammonia is not. ✗

Answer: C. Chlorine and sulphur (IV) oxide.

Tip: Remember that Cl₂ bleaches by oxidation and SO₂ bleaches by reduction. Whenever you see both in one option, it is likely the answer to a bleaching question. Ammonia and H₂S are never bleaching agents.