The correct option is **B. the rare gases**. ### Detailed Explanation: To understand why the correct answer is B, we need to analyze the process described in the question step by step. 1. **Composition of Air**: - Air is primarily composed of nitrogen (approximately 78%), oxygen (approximately 21%), argon (approximately 0.93%), carbon dioxide (approximately 0.04%), and trace amounts of other gases, including water vapor. 2. **Passing Air Through Alkaline Pyrogallol**: - Alkaline pyrogallol is a solution that is used to absorb oxygen from the air. When air is passed through alkaline pyrogallol, the oxygen reacts with the pyrogallol, effectively removing it from the gas mixture. The reaction can be simplified as: \[ \text{O}_2 + \text{pyrogallol} \rightarrow \text{products (absorbed)} \] - After this step, the remaining gases in the mixture will primarily be nitrogen, carbon dioxide, water vapor, and the rare gases (like argon). 3. **Passing Air Over Quicklime**: - Quicklime (calcium oxide, CaO) is a strong desiccant and also reacts with carbon dioxide to form calcium carbonate (CaCO₃). The reaction can be represented as: \[ \text{CaO} + \text{CO}_2 \rightarrow \text{CaCO}_3 \] - This means that when the remaining gases (after the alkaline pyrogallol) are passed over quicklime, the carbon dioxide is absorbed and removed from the gas mixture. 4. **Final Composition of Gases**: - After both treatments (alkaline pyrogallol and quicklime), the gases that remain are nitrogen and the rare gases (like argon). However, since the question specifically asks for the gases left after both treatments, we must consider that carbon dioxide and oxygen have been removed. ### Why Other Options Are Incorrect: - **Option A: Nitrogen and Carbon Dioxide**: - This option is incorrect because carbon dioxide is absorbed by quicklime, so it cannot be present in the final gas mixture. - **Option C: Nitrogen and Oxygen**: - This option is incorrect because oxygen is absorbed by alkaline pyrogallol, so it will not be present in the final gas mixture. - **Option D: Nitrogen and the Rare Gases**: - While this option seems plausible, it does not specify that the only gases left are the rare gases. The correct answer must focus on the fact that nitrogen is also present along with the rare gases, making this option misleading. ### Summary: - Air contains nitrogen, oxygen, carbon dioxide, water vapor, and rare gases. - Alkaline pyrogallol absorbs oxygen from the air. - Quicklime absorbs carbon dioxide from the remaining gases. - The final gases left after both treatments are nitrogen and the rare gases. ### Revision Summary: - Alkaline pyrogallol removes oxygen from air. - Quicklime absorbs carbon dioxide from the remaining gases. - The gases left after both treatments are nitrogen and rare gases. - Understanding the reactions involved is crucial for determining the final gas composition.