Sulphur dioxide is a more powerful reducing agent in the alkaline medium than in the acidic medium. Assign reason.

Explanation

The reducing nature of `SO_(2)` in the alkaline medium is shown by the following equation.
`SO_(2)+2OH^(-) harr SO_(4)^(2-)+2H^(+)+2e^(-)`
The addition of acid `(H^(+))` favours the reverse reaction. Therefore, sulphur dioxide fails to act as reducing agent in the acidic medium. In the alkaline medium, `H^(+)` ions formed as the products are removed. This favours the forward reaction. As a result, `SO_(2)` acts as a reducing agent in the alkaline medium.