Question

In which of the following reactions, there is no change in valency ?

• A. ${4 KClO3 -> 3KClO4 + KCl }$
• B. ${SO2 + 2H2S -> 2H2O + 3S }$
• C. ${ BaO2 + H2SO4 -> BaSO4 + H2O2}$
• D. ${ 3 BaO + O2 -> 2 BaO2}$

Answer 1

The Correct Option is C

To determine in which reaction there is no change in valency, we must check if the oxidation states (valencies) of the elements involved remain unchanged before and after the reaction. Let's analyze each reaction step by step:

1. {4 KClO_3 \rightarrow 3 KClO_4 + KCl}

   In this reaction, the oxidation state of chlorine in {KClO_3} is +5, in {KClO_4} it is +7, and in {KCl} it is -1. Thus, there is a change in the valency of chlorine as it gets both oxidized and reduced (disproportionation reaction).

2. {SO_2 + 2H_2S \rightarrow 2H_2O + 3S}

   In this reaction, the oxidation state of sulfur in {SO_2} is +4 and in {H_2S} is -2. After the reaction, in elemental sulfur (S), the oxidation state is 0. Therefore, sulfur undergoes a change in oxidation state, indicating a redox process.

3. {BaO_2 + H_2SO_4 \rightarrow BaSO_4 + H_2O_2}

   For this reaction, the oxidation state of barium (Ba) is +2 throughout the reaction, as it remains in both {BaO_2} and {BaSO_4} as +2. Similarly, oxygen's oxidation numbers remain consistent in the molecular structures. Therefore, there is no change in the valency for the elements involved in this reaction.

4. {3 BaO + O_2 \rightarrow 2 BaO_2}

   In the conversion of {BaO} to {BaO_2}, the oxidation state of barium remains +2. However, the oxidation state of oxygen in molecular {O_2} (0) and in {BaO_2} (-1) indicates a change in valency.

From the above analysis, we conclude that the only reaction with no change in valency is:

The correct answer is:
{BaO_2 + H_2SO_4 \rightarrow BaSO_4 + H_2O_2}