Name the gas that can readily decolourise acidified `KMnO_(4)` solution:

Options

A. `SO_(2)`
B. `NO_(2)`
C. `P_(2) O_(5)`
D. `CO_(2)`

Answer

A

Explanation

In presence of moisture, `SO_(4)` acts as a good reducing agent. Its reducing character is due to evoution of nascent hydrogen:
`SO_(2) + 2H_(2) O rarr H_(2) SO_(4) + 2 [H]`
It decolurises pind violet colour of acidified `KMnO_(4)` solution
`2 KMnO_(4) + 3 H_(2) SO_(4) rarr K_(2) SO_(4) + 2 MnSO_(4) + 3 H_(2) O + 5[O]`
`underline(SO_(2) + H_(2) O + [O] rarr H_(2) SO_(4) xx 5)`
`underset("Pink violet")(2KMnO_(4) + 5 SO_(2)) rarr K_(2) SO_(4) _ underset("colorless")(2MnSO_(4)) + 2 H_(2) SO_(4)`