\(\text{S}{{\text{O}}_{2}}+2{{\text{H}}_{2}}\text{O}\to {{\text{H}}_{2}}\text{S}{{\text{O}}_{4}}+\,\underset{nascent\,\,\,hydrogen}{\mathop{2H}}\,\)

Thus, \(\mathrm{SO}_{2}\) in presence of moisture is used as bleaching agent. This is due to the reducing nature of \(\mathrm{SO}_{2}-\) For delicate articles

                Coloured matter \(+\mathrm{H} \longrightarrow\) Colourless matter

Similarly, \(\mathrm{Cl}_{2}\) acts as bleaching agent in presence of moisture

                            \(\text{C}{{\text{l}}_{2}}+{{\text{H}}_{2}}\text{O}\to 2\text{HCl}+[\text{O}]\)

                 Coloured matter \(+\,[O]\,\to \) Colourless matter