### Correct Option: D. Rare gases ### Explanation of the Correct Answer When nitrogen is obtained from the liquefaction of air, it is separated from the other components of air, which include oxygen, argon, carbon dioxide, and trace amounts of other gases. The process of liquefaction involves cooling air to very low temperatures, causing it to condense into a liquid. As the air is cooled, different gases condense at different temperatures due to their varying boiling points. 1. **Composition of Air**: Air is primarily composed of nitrogen (approximately 78%), oxygen (about 21%), and other gases like argon (around 0.93%), carbon dioxide (0.04%), and trace amounts of rare gases (like neon, helium, and krypton). 2. **Density of Nitrogen from Air**: When nitrogen is extracted from liquefied air, it is relatively pure nitrogen, but it may also contain small amounts of other gases that were present in the air, including rare gases. The presence of these rare gases can slightly increase the overall density of the nitrogen obtained from this method. 3. **Density of Nitrogen from Compounds**: On the other hand, nitrogen obtained from nitrogen-containing compounds (like ammonia or nitrates) is typically very pure nitrogen gas (N₂) with minimal impurities. This nitrogen is less dense because it lacks the additional components (like rare gases) that can contribute to the overall density when nitrogen is extracted from air. ### Why the Other Options are Incorrect - **A. Water Vapour**: While water vapor can be present in the air, it is not a significant contributor to the density of nitrogen. In fact, water vapor is less dense than nitrogen gas. When air is liquefied, water vapor condenses out before nitrogen, so it does not contribute to the density of nitrogen obtained from liquefaction. - **B. Oxygen**: Oxygen is a major component of air, but when nitrogen is separated from air, oxygen is removed. The nitrogen obtained from liquefaction is primarily nitrogen gas (N₂) and does not contain oxygen. Therefore, oxygen cannot be a reason for the higher density of nitrogen obtained from liquefaction. - **C. Carbon (IV) Oxide**: Carbon dioxide (CO₂) is present in very small amounts in the atmosphere. While it is denser than nitrogen, it is not a significant component of the nitrogen obtained from liquefaction. Moreover, during the liquefaction process, CO₂ is typically removed along with other gases, so it does not contribute to the density of the nitrogen obtained. ### Summary of Key Points - Nitrogen from liquefaction of air contains rare gases, which can increase its density. - Nitrogen from compounds is usually purer and lacks these additional gases, making it less dense. - Water vapor and oxygen do not contribute to the density of nitrogen obtained from air. - Carbon dioxide is present in negligible amounts and is typically removed during the liquefaction process. ### Revision Summary - Nitrogen from liquefaction of air contains rare gases, increasing its density. - Pure nitrogen from compounds lacks these additional gases, resulting in lower density. - Water vapor and oxygen do not contribute to the density of nitrogen from air. - Carbon dioxide is minimal and usually removed during liquefaction.