Question

Which of the following reactions exhibits the reducing property of ozone ?

• A. \(\text{NO}\text{(g)}+\text{O}_3\text{(g)}⟶\text{NO}_2\text{(g)}+\text{O}_2\text{(g)}\)
• B. \(2\text{KI}\text{(aq)}+\text{H}_2\text{O}\text{(l)}+\text{O}_3\text{(g)}⟶2\text{KOH}\text{(aq)}+\text{I}_2\text{(g)}+\text{O}_2\text{(g)}\)
• C. \(\text{H}_2\text{O}_2\text{(l)}+\text{O}_3\text{(g)}⟶\text{H}_2\text{O}\text{(l)}+2\text{O}_2\text{(g)}\)
• D. \(\text{PbS}\text{(s)}+4\text{O}_3\text{(g)}⟶\text{PbSO}_4\text{(s)}+4\text{O}_2\text{(g)}\)

Hint:

Ozone usually oxidises. Its reducing action is seen with hydrogen peroxide, giving water and oxygen.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Ozone is mostly an oxidising agent because it readily gives up an oxygen atom. Its reducing action is the rare case and is shown only with a few compounds such as \(\text{H}_2\text{O}_2\).

Step 2: Key Formula or Approach:
Decide in each reaction whether the other reactant is being oxidised (then ozone is oxidising) or reduced (then ozone is reducing).

Step 3: Check reaction (A):
\(\text{NO} + \text{O}_3 \to \text{NO}_2 + \text{O}_2\): NO is oxidised to \(\text{NO}_2\), so ozone acts as an oxidising agent.

Step 4: Check reactions (B) and (D):
\(2\text{KI} + \text{H}_2\text{O} + \text{O}_3 \to 2\text{KOH} + \text{I}_2 + \text{O}_2\): iodide is oxidised to iodine, so ozone is oxidising.
\(\text{PbS} + 4\text{O}_3 \to \text{PbSO}_4 + 4\text{O}_2\): sulphide is oxidised to sulphate, so ozone is oxidising.

Step 5: Check reaction (C):
\(\text{H}_2\text{O}_2 + \text{O}_3 \to \text{H}_2\text{O} + 2\text{O}_2\): here the peroxide is reduced to water and oxygen is evolved from both reactants. This is the standard textbook example of the reducing action of ozone, in which it reduces hydrogen peroxide.

Final Answer:
The reducing property of ozone is shown by its reaction with hydrogen peroxide, option (C). \[ \boxed{\text{H}_2\text{O}_2+\text{O}_3\to\text{H}_2\text{O}+2\text{O}_2 \text{ (C)}} \]