Chlorine water is used as a bleaching agent because it is

Step 1: Analyze the question The question asks why chlorine water bleaches. We need the chemical property responsible for the bleaching action.

Step 2: The concept When chlorine dissolves in water, it reacts to form two acids:

Cl₂ + H₂O ⇌ HCl + HOCl (hypochlorous acid)

Hypochlorous acid is unstable and releases nascent (atomic) oxygen:

HOCl → HCl + [O]

The nascent oxygen oxidizes coloured substances (dyes and pigments) into colourless compounds. This is bleaching by oxidation.

Step 3: Check each option

• A. An acidic solution: Chlorine water is acidic, but acidity is not what removes colour. Many acids do not bleach at all.
• B. An alkaline solution: Wrong. Chlorine water is acidic, not alkaline.
• C. An oxidizing agent: Correct. The nascent oxygen from HOCl oxidizes the coloured matter and destroys the colour.
• D. A reducing agent: Wrong. Sulphur dioxide bleaches by reduction, but chlorine does not.

Step 4: Answer The correct answer is C. An oxidizing agent.

Tip: Remember "Chlorine bleaches by Oxidation, Sulphur dioxide bleaches by Reduction." Also, chlorine's bleaching is permanent, while SO₂'s bleaching is temporary because the colour can return when the material is exposed to air (oxygen). Moist or damp litmus paper or coloured flowers placed in chlorine lose their colour, but dry chlorine does not bleach, which shows that water is needed to form HOCl.