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.