On charging the lead storage battery, the oxidation state of lead changes from x₁ to y₁ at the anode and from x₂ to y₂ at the cathode. The values of x₁, y₁, x₂, y₂ are respectively :

Solution

Chemistry ma’am · 4 steps

Charging just runs the discharge backwards: lead sulphate on both plates turns back into Pb and PbO2.

1. Discharged state. After discharge, both plates are coated with PbSO₄, where lead is +2. So on charging, both electrodes start at +2: x₁ = x₂ = +2.
2. Naming the plates. The battery's anode is the spongy lead plate (the negative terminal). Its cathode is the PbO₂ plate (the positive terminal). The plates keep these names while charging, even though the reactions reverse.

   PbSO₄ + 2e⁻ → Pb + SO₄²⁻ PbSO₄ + 2H₂O → PbO₂ + SO₄²⁻ + 4H⁺ + 2e⁻

3. Read off changes. At the anode (lead plate), PbSO₄ becomes Pb: +2 → 0. At the cathode (PbO₂ plate), PbSO₄ becomes PbO₂: +2 → +4.
4. So. x₁, y₁, x₂, y₂ = +2, 0, +2, +4, which is option (d).

The idea to keep. In the lead storage battery, PbSO₄ (+2) is the meeting point. Discharge sends Pb (0) and PbO₂ (+4) towards +2, and charging pulls them back apart.

Answer from the NTA final answer key. Solution by PrepWiser.