How is the presence of `SO_2` detected?

Explanation

`SO_2` is a pungent smelling gas. Two tests are used to detect the presence of `SO_2` that are as follows:
(i) `SO_2` turns the pink-violet colour of `KMnO_4` solution colourless due to the reduction of `MnO_4^(-)` to `Mn^(2+)`.
`5SO_2 + underset("(Pink-Violet)")(2MnO_4^(-)) + 2H_2O rarr 5SO_4^(-) + 4H^(+) + underset("(Colourless)")(2Mn^(2+))`
(ii) `SO_2` turns orange coloured acidified `K_2Cr_2O_7` solution green due to the reduction of `Cr_2O_7^(2-)` to `Cr^(3+)` ion.
`3SO_2+underset("(Orange)")(Cr_2O_7^(2-)) +2H^(+) rarr 3SO_4^(2-)+H_2O+ underset("(Green)")(2Cr^(3+))`