What chemical changes occur at the anode and cathode when a secondary lead storage battery is recharged by connecting it to an external direct current power source?

Answer and explanation

Correct answer: C. PbSO4 on anode is reduced to spongy Pb; PbSO4 on cathode oxidizes to PbO2 to regenerate sulfuric acid

- At the negative electrode: (reduction),
- At the positive electrode: (oxidation).
  1. Step 1: During discharge of a lead-acid battery, both electrodes are converted into insoluble lead sulfate: , depleting and lowering its density.
  2. Step 2: During recharging, an external DC current forces the reverse electrochemical reactions:
  3. Step 3: The overall recharging reaction is: , restoring the electrodes and replenishing sulfuric acid concentration.
Answer
Lead sulfate (PbSO4) on the anode is reduced to spongy lead (Pb), and PbSO4 on the cathode is oxidized to lead dioxide (PbO2), regenerating sulfuric acid
Why not the others: 'Spongy lead is converted into lead sulfate...' describes discharging, not recharging; 'Lead dioxide is converted into sulfur dioxide...' does not occur in lead storage batteries; 'Water converted into heavy water...' is scientifically nonsensical.

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