It involves the following steps:
(i) Chlorine reacts with water to form hydrochloric acid and hypochlorous acid.
                 ...(1)
(ii) Hydrochloric acid then reacts with sodium hydroxide to give sodium chloride and water.
                ...(2)
(iii) Hypochlorous acid reacts with sodium hydroxide to give sodium hypochlorite and water.
               ...(3)
(iv) Sodium hypochlorite decomposes to give sodium chlorate.

Multiply the partial equations (1), (2) and (3) by 3 and add all the four equations.