Chem 二問

SO2­ can decolorize acidified KMnO4 solution. The reaction is redox, because acidified KMnO4 solution is a strong oxidizing agent and SO2 is a reducing agent.
5SO2(g) + 2H2O(l) + 2MnO4-(aq) → 2Mn2+(aq) + 5SO42-(aq) + 4H+(aq)

Chlorine water is a mixture. Chlorine water is formed by dissolving chlorine in water.
Besides, chlorine reacts with water reversibly.
Cl2(aq) + H2O(l) = HCl(aq) + HOCl(aq)
Therefore, chlorine water is a mixture containing water, chlorine, hydrochloric acid (HCl(aq)), and chlorous acid (HOCl(aq)).

Chlorine water do not react with sodium chloride. Therefore, there is no observable change.