Chlorine water is added dropwise to potassium iodide solution containing starch. First a blue colour appears. On adding a large excess of chlorine water the blue colour disappears because

1. A$\mathrm{I}{}_2$ is further oxidised to $\mathrm{HIO}{}_3$
2. B$\mathrm{I}{}_2$ is reduced back to $\mathrm{I}{}^{-}$
3. Cstarch is decomposed by $\mathrm{HCl}$
4. D$\mathrm{I}{}_2$ sublimes away