In this question, we need to identify the gas that can readily decolourise acidified potassium permanganate (\(KMnO_4\)) solution. Let's analyze each option to determine the correct answer:
Thus, the gas that can readily decolourise acidified \(KMnO_4\) solution is $SO_2$. This is because \(SO_2\) is a strong reducing agent and reacts effectively with \(KMnO_4\) to change its oxidation state, leading to decolourisation.