Two Half Cell reactions are as,
Reduction: PbO₂ + 2e⁻ → Pb²⁺
As it is acidic medium reaction, so add H⁺ on reactant side as it has more number of oxygen atoms and add H₂O on product side, and balance tehe elements, So,
4 H⁺ + PbO₂ + 2e⁻ → Pb²⁺ + 2 H₂O (1)
Oxidation: I⁻ → I₂ + 1e⁻
Balance Number of elements along with electrons,
2 I⁻ → I₂ + 2e⁻ (2)
Compare eq. 1 and 2,
4 H⁺ + PbO₂ + 2e⁻ → Pb²⁺ + 2 H₂O
2 I⁻ → I₂ + 2e⁻
⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻
PbO₂ + 2 I⁻ + 4 H⁺ → Pb²⁺ + I₂ + 2H₂O
Number of Coefficients = 11
