In which of the following reactions, there is no change in valency? (a) SO 2H S 2H O 3S → (b) 2Na O 2Na O → (c) Na O H SO Na SO H O → (d) 4KClO 3KClO KCl → Ans (c) Sol. The oxidation states of central atom in each given options is as follows: S O 2H S 2H O 3S 2Na O 2N a O N a O H SO N a SO H O 4KC l O 3KC l O KC l → → → → Clearly, in option (c) there is no change in oxidation state of sodium. Therefore, (c) is the correct answer.