Identify the oxidation and reduction half-reactions. IO3⁻ is reduced to I2, and H2SO3 is oxidized to SO4²⁻.
Write the reduction half-reaction: IO3⁻ → I2. Balance iodine atoms first, then add electrons to balance the charge.
Write the oxidation half-reaction: H2SO3 → SO4²⁻. Balance sulfur atoms first, then add electrons to balance the charge.
Balance oxygen atoms by adding H2O molecules to the side that needs oxygen. Then balance hydrogen atoms by adding H⁺ ions.
Combine the balanced half-reactions, ensuring that the number of electrons lost in oxidation equals the number gained in reduction. Adjust coefficients to achieve this balance.