Bleaching action of SO₂ is:

A) permanent, reduction

B) temporary, reduction

C) permanent, oxidation

D) temporary, oxidation

Sulphur dioxide is a temporary bleaching agent, unlike Chlorine, which is a permanent bleaching agent! This is because the mechanism for bleaching is different:

SO2-Reduction => TEMPORARY
Cl2-Oxidation => PERMANENT
Sulphur dioxide removes oxygen from the coloured substance and makes it colourless. But atmospheric oxygen slowly takes place of the removed oxygen and because of which the material regains the colour.