How does H2O2 behave as a bleaching agent?
H2O2 or hydrogen peroxide acts as a strong oxidizing agent both in acidic and basic media.
When added to a cloth, it breaks the chemical bonds of the chromophores (colour producing agents). Hence, the visible light is not absorbed and the cloth gets whitened.
Bleaching action of H2O2 is due to the oxidation of colouring matter by nascent oxygen.
H2O2(Z) ———> H2O(Z) + O(g)