Chlorine is used to purify drinking water. Excess of chlorine is harmful. The excess of chlorine is removed by treating with sulphur dioxide. Present a balanced equation for this redox change taking place in water.

(N/A) The given redox reaction can be represented as:
$Cl_{2(aq)} + SO_{2(aq)} + 2H_2O_{(l)} \to 2Cl^{-}_{(aq)} + SO_{4(aq)}^{2-} + 4H^{+}_{(aq)}$
The oxidation half-reaction is:
$\overset{+4}{S}O_{2(aq)} \to \overset{+6}{S}O_{4(aq)}^{2-}$
Balancing the oxidation number by adding two electrons:
$SO_{2(aq)} \to SO_{4(aq)}^{2-} + 2e^-$
Balancing the charge by adding $4H^{+}$ ions:
$SO_{2(aq)} \to SO_{4(aq)}^{2-} + 4H^{+}_{(aq)} + 2e^-$
Balancing $O$ atoms and $H^{+}$ ions by adding $2H_2O$ molecules:
$SO_{2(aq)} + 2H_2O_{(l)} \to SO_{4(aq)}^{2-} + 4H^{+}_{(aq)} + 2e^- \quad \dots(i)$
The reduction half-reaction is:
$Cl_{2(aq)} \to Cl^{-}_{(aq)}$
Balancing chlorine atoms:
$\overset{0}{Cl}_{2(aq)} \to 2\overset{-1}{Cl}^{-}_{(aq)}$
Balancing the oxidation number by adding electrons:
$Cl_{2(aq)} + 2e^- \to 2Cl^{-}_{(aq)} \quad \dots(ii)$
Adding equation $(i)$ and $(ii)$ gives the balanced chemical equation:
$Cl_{2(aq)} + SO_{2(aq)} + 2H_2O_{(l)} \to 2Cl^{-}_{(aq)} + SO_{4(aq)}^{2-} + 4H^{+}_{(aq)}$