### Correct Option: D. Nitrogen and the rare gases ### Detailed Explanation: To understand why the correct answer is D (nitrogen and the rare gases), 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 (about 21%), argon (a rare gas, about 0.93%), carbon dioxide (around 0.04%), and trace amounts of other gases including water vapor. 2. **Passing Air Through Alkaline Pyrogallol**: - Alkaline pyrogallol is a solution that reacts with oxygen. When air is passed through alkaline pyrogallol, the oxygen in the air reacts with the pyrogallol, effectively removing it from the gas mixture. The reaction can be summarized as follows: \[ \text{O}_2 + \text{pyrogallol} \rightarrow \text{products (consumed O}_2\text{)} \] - After this step, the remaining gases in the mixture will be nitrogen, carbon dioxide, water vapor, and the rare gases. 3. **Passing Air Over Quicklime**: - Quicklime (calcium oxide, CaO) is a strong desiccant and reacts with carbon dioxide to form calcium carbonate (CaCO₃). The reaction is: \[ \text{CaO} + \text{CO}_2 \rightarrow \text{CaCO}_3 \] - This means that when the remaining gases (after the alkaline pyrogallol) are passed over quicklime, the carbon dioxide is removed from the gas mixture. 4. **Final Composition of Gases**: - After both treatments (alkaline pyrogallol and quicklime), the gases that remain are nitrogen (which does not react with either alkaline pyrogallol or quicklime) and the rare gases (like argon, which are inert and do not react with these substances). ### Why Other Options Are Incorrect: - **Option A: Nitrogen and carbon dioxide**: - This option is incorrect because carbon dioxide is removed when the air is passed over quicklime. Therefore, carbon dioxide cannot be present in the final gas mixture. - **Option B: The rare gases**: - While the rare gases will indeed be present, this option is incomplete. It does not account for nitrogen, which is also present after the removal of oxygen and carbon dioxide. - **Option C: Nitrogen and oxygen**: - This option is incorrect because oxygen is removed during the first step with alkaline pyrogallol. Thus, oxygen cannot be part of the final gas mixture. ### Summary of Key Points: - Air contains nitrogen, oxygen, carbon dioxide, water vapor, and rare gases. - Alkaline pyrogallol removes oxygen from the air. - Quicklime removes carbon dioxide from the remaining gases. - The final gases left after both treatments are nitrogen and the rare gases. ### Revision Summary: - Air is primarily composed of nitrogen and oxygen, with small amounts of carbon dioxide and rare gases. - Alkaline pyrogallol removes oxygen from the air. - Quicklime reacts with and removes carbon dioxide. - The final gases remaining after both treatments are nitrogen and the rare gases.