Classical Idea Of Redox Reactions Oxidation And Reduction Reactions

Definition: A redox reaction involves a change in oxidation states of elements — one species gets oxidized (loses electrons), and another gets reduced (gains electrons).

Option 1: NaCl dissolving in water

This is a physical change, not a redox reaction. No change in oxidation numbers.

Option 2:

Oxidation number of O in is -1. In , it's -2, and in , it's 0.

• Some oxygen atoms are reduced: -1 → -2
• Others are oxidized: -1 → 0

✔ This is a **disproportionation redox reaction**.

Option 3: NaOH dissolving in water

Again, only dissociation. No redox — no oxidation number change.

Option 4:

This is a thermal decomposition reaction, but oxidation states remain:

• Ca: +2 → +2
• C: +4 → +4
• O: -2 in all species

❌ Not a redox reaction.

✅ Correct Answer:

Option 2: