The correct option for restoring humid air polluted by chlorine is **B. acidified KMnO\(_{4}\)**. Let's break down why this is the correct answer and why the other options are not suitable. ### Explanation of the Correct Answer (B: Acidified KMnO\(_{4}\)) 1. **Understanding Chlorine Pollution**: Chlorine (Cl\(_2\)) is a toxic gas that can cause respiratory issues and other health problems when present in humid air. It is a strong oxidizing agent and can react with various substances. 2. **Role of Acidified KMnO\(_{4}\)**: Potassium permanganate (KMnO\(_{4}\)) is a powerful oxidizing agent. When it is acidified (usually with sulfuric acid, H\(_2\)SO\(_4\)), it can effectively react with chlorine gas. The reaction can be summarized as follows: \[ 2 \text{KMnO}_4 + 16 \text{H}^+ + 5 \text{Cl}_2 \rightarrow 2 \text{Mn}^{2+} + 8 \text{Cl}^- + 8 \text{H}_2\text{O} \] In this reaction, chlorine is reduced to chloride ions (Cl\(^-\)), which are much less harmful. The manganese in KMnO\(_{4}\) is reduced from Mn(VII) to Mn(II), which is a less reactive form. 3. **Effectiveness**: The acidified KMnO\(_{4}\) not only neutralizes chlorine but also helps in purifying the air by converting harmful chlorine gas into harmless chloride ions. ### Why the Other Options Are Incorrect **A. Solid MnO\(_{2}\)**: - **Reasoning**: Manganese dioxide (MnO\(_2\)) is not a strong oxidizing agent in the same way that KMnO\(_{4}\) is. While it can react with chlorine, it does not do so effectively in humid air. It is also less soluble and would not interact with chlorine gas in the air as effectively as acidified KMnO\(_{4}\). **C. Acidified FeSO\(_{4}\)**: - **Reasoning**: Acidified iron(II) sulfate (FeSO\(_{4}\)) is a reducing agent, but it does not have the same oxidizing power as KMnO\(_{4}\). It may not effectively react with chlorine to neutralize it. Instead, it could potentially lead to the formation of iron(III) ions, which do not help in removing chlorine from the air. **D. Saturated NaCl(aq)**: - **Reasoning**: Saturated sodium chloride solution (NaCl) would not react with chlorine gas. Instead, it would simply add more chloride ions to the environment without neutralizing the chlorine gas. This option does not address the pollution problem effectively. ### Summary of Key Points - **Correct Answer**: B. Acidified KMnO\(_{4}\) effectively neutralizes chlorine gas in humid air. - **Reaction**: KMnO\(_{4}\) reacts with chlorine, converting it to harmless chloride ions. - **Other Options**: A (MnO\(_2\)) is ineffective, C (FeSO\(_{4}\)) does not neutralize chlorine, and D (NaCl) does not react with chlorine. - **Importance of Oxidizing Agents**: Understanding the role of oxidizing agents like KMnO\(_{4}\) is crucial in environmental chemistry for pollution control. This thorough understanding of the reactions and properties of the substances involved will help you in your revision and preparation for exams in chemistry.