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 redox reaction involves the oxidation of $SO_2$ to $SO_4^{2-}$ and the reduction of $Cl_2$ to $Cl^-$.
$1.$ Oxidation Half-Reaction $(O.H.R.)$: $SO_{2(aq)} + 2H_2O_{(l)} \rightarrow SO_{4(aq)}^{2-} + 4H^+_{(aq)} + 2e^-$
$2.$ Reduction Half-Reaction $(R.H.R.)$: $Cl_{2(g)} + 2e^- \rightarrow 2Cl^-_{(aq)}$
Adding both half-reactions to cancel the electrons:
$SO_{2(aq)} + Cl_{2(g)} + 2H_2O_{(l)} \rightarrow SO_{4(aq)}^{2-} + 4H^+_{(aq)} + 2Cl^-_{(aq)}$