JEE Main 2021 · 26 February · morning · Single correct · +4 / −1
Compound A used as a strong oxidizing agent is amphoteric in nature. It is the part of lead storage batteries. Compound A is :
- (a) PbO
- (b) PbO₂
- (c) PbSO₄
- (d) Pb₃O₄
Answer and solution
Answer (b) PbO₂
Solution
Chemistry ma’am · 4 steps
Lead badly wants to drop from +4 to +2, and that pull is what makes PbO₂ the oxidiser here.
- Inert pair effect. Down group 14, the 6s² pair of lead resists bonding, so Pb²⁺ is more stable than Pb⁴⁺. A lead(IV) compound readily gains electrons to reach +2, so it is a strong oxidising agent.
- Amphoteric nature. PbO₂ reacts with acids and also with alkalis. With hot NaOH it forms a plumbate: PbO₂ + 2NaOH → Na₂PbO₃ + H₂O. With HCl it reacts and frees chlorine: PbO₂ + 4HCl → PbCl₂ + Cl₂ + 2H₂O.
- Lead storage battery. The cathode plate is coated with PbO₂. On discharge it is reduced: PbO₂ + SO₄²⁻ + 4H⁺ + 2e⁻ → PbSO₄ + 2H₂O.
Compound Strong oxidiser? Amphoteric oxide? Battery electrode material? PbO (Pb +2) No, Pb is already in its stable +2 state Yes No PbO₂ (Pb +4) Yes Yes Yes, the cathode PbSO₄ (Pb +2) No No, it is a salt Only a discharge product Pb₃O₄ (mixed oxide) Some, from its Pb(IV) part Not the usual example No - So. Only PbO₂ fits all three clues, so compound A is (b).
The idea to keep. For lead, +2 is the stable state because of the inert pair effect. Any Pb(IV) compound, especially PbO₂, acts as an oxidiser. PbO₂ is also the cathode of the lead storage battery.
Answer from the NTA final answer key. Solution by PrepWiser.