Question

Name the gas that can readily decolourises acidified KMnO₄ solution.

Options

• CO₂

• SO₂

• NO₂

• P₂O₅

Answer 1

SO₂

Explanation:

Sulphur dioxide (SO₂) is a reducing gas that can readily decolourise acidified potassium permanganate (KMnO₄) solution. This happens because SO₂ reduces the purple permanganate ion (\[\ce{MnO^-_4}\]) to the nearly colorless Mn²⁺ ion, causing the decolourisation of the solution. Other gases like CO₂, NO₂, and P₂O₅ do not have this reducing property and thus cannot decolourise acidified KMnO₄ readily.