Question

Observe the following reactions
(i) \( 2\text{KClO}_3(s) \xrightarrow{\Delta} 2\text{KCl}(s) + 3\text{O}_2(g) \)
(ii) \( 2\text{H}_2\text{O}_2(aq) \xrightarrow{\Delta} 2\text{H}_2\text{O}(l) + \text{O}_2(g) \)
(iii) \( \text{AgNO}_3(aq) + \text{KCl}(aq) \longrightarrow \text{AgCl}(s) + \text{KNO}_3(aq) \)
(iv) \( 2\text{Na}(s) + \frac{1}{2} \text{O}_2(g) \longrightarrow \text{Na}_2\text{O}(s) \)
The number of redox reactions in this list is

• A. \( 3 \)
• B. \( 4 \)
• C. \( 2 \)
• D. \( 1 \)

Hint:

In a redox reaction, there is a change in oxidation states.

Answer 1

The Correct Option is A

A redox reaction involves a change in oxidation states.

(i) \( 2\text{KClO}_3(s) \xrightarrow{\Delta} 2\text{KCl}(s) + 3\text{O}_2(g) \)
Oxidation state of Cl in KClO₃ is +5, and in KCl is -1.
Oxidation state of O in KClO₃ is -2, and in O₂ is 0.
This is a redox reaction.

(ii) \( 2\text{H}_2\text{O}_2(aq) \xrightarrow{\Delta} 2\text{H}_2\text{O}(l) + \text{O}_2(g) \)
Oxidation state of O in H₂O₂ is -1, in H₂O is -2, and in O₂ is 0.
This is a redox reaction.

(iii) \( \text{AgNO}_3(aq) + \text{KCl}(aq) \longrightarrow \text{AgCl}(s) + \text{KNO}_3(aq) \)
Oxidation states: Ag(+1), N(+5), O(-2), K(+1), Cl(-1).
Oxidation states do not change.
This is not a redox reaction.

(iv) \( 2\text{Na}(s) + \frac{1}{2} \text{O}_2(g) \longrightarrow \text{Na}_2\text{O}(s) \)
Oxidation state of Na is 0, in Na₂O is +1.
Oxidation state of O is 0, in Na₂O is -2.
This is a redox reaction.

The redox reactions are (i), (ii), and (iv).
Thus, there are 3 redox reactions.