Bleaching of flowers by chlorine is permanent while that by sulphur dioxide is temporary. Explain.

Explanation

`Cl_2` bleaches coloured material by oxidation as shown below
`Cl_2 + H_2 O to 2HCl + [O]`
Coloured material + [O] `to` Coloured material
As air cannot reduce the colourless material to coloured material bleaching is permanent. On the other hand `SO_2` bleaches coloured material by reduction and hence bleaching is temporary since when the bleached colourless material is exposed to air, it gets oxidised and the colour is restored.
`SO_2 + 2H_2 O to 2H_2 SO_4 + 2[H]`
Coloured material + [H] `to` Colourless material `underset("oxidation")overset("Aerial")to ` Coloured material .