The bleaching action of moist sulphur dioxide is due to

Aoxidation
Badsorption
Creduction
Dhydrolysis

Answer: C

In the presence of water SO2 acts as a reducing agent and decolourises the dye by reduction. The colour often returns on standing in air as the dye is re-oxidised.

Practice p-Block Elements: Groups 15 and 16 More on Sulphur allotropes, SO2, sulphuric acid, oxyacids of sulphur

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