In the treatment of domestic water supplies, chlorine is added to the water to form chloric(I) acid,HClO.

Cl2(aq) + H2O(I) → H+(aq) + Cl–(aq) + HClO(aq)

The HClO reacts further to give the chlorate(I) ion.(CLO-)

HClO(aq) + H2O(I) → H3O+(aq) + ClO–(aq)

Both HClO and ClO–kill bacteria by oxidation.

What is the change in oxidation number of chlorine in forming the chlorate(I) ion from the aqueous chlorine?

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