How is the presence of `SO_2` detected?

Explanation

`SO_2` acts as a reducing agent hence `SO_2` turns pink coloured `KMnO_4` to colourless solution due to reduction of `MnO_4^(ɵ)` to `Mn^(2+)`
`[MnO_4^(ɵ)+8H^(ɵ)+5e^(ɵ)toMn^(2+)+4H_2O]xx2`
`underline[SO_2+2H_2OtoSO_4^(2-)+4H^(o+)2e^(ɵ)]xx5)`
`underline(2MnO_4^(ɵ)+2H_2O+5SO_2to2Mn^(2+)+5SO_4^(2-)+4H^(o+))`