Explanation

(c)
The pair of SO_{2} and Cl_{2} has bleaching property.
In presence of moisture, SO_{2} acts as a bleaching agent.
SO_{2}+2H_{2}O⟶H_{2}SO_{4}+2[H]
The nascent hydrogen bleaches the colour of the substance, thus SO_{2} bleaches by reduction while Cl_{2} bleaches by oxidation.
H_{2}O + Cl_{2}⟶HCl + HClO
HClO ⟶HCl + [O]
[O] + coloured substance ⟶colourless substances