The correct option is **A. ammonia**. ### Detailed Explanation: 1. **Understanding Solubility**: - Solubility refers to the ability of a substance (solute) to dissolve in a solvent (like water). The solubility of gases in water can vary significantly based on their chemical properties and interactions with water molecules. 2. **Ammonia (NH₃)**: - Ammonia is a polar molecule due to the difference in electronegativity between nitrogen and hydrogen. This polarity allows ammonia to form hydrogen bonds with water molecules, which significantly enhances its solubility. - At room temperature, ammonia is highly soluble in water, with a solubility of about 33% by weight. This means that a considerable amount of ammonia can dissolve in water, making it a common compound in various applications, including fertilizers and cleaning agents. 3. **Carbon Dioxide (CO₂)**: - Carbon dioxide is also soluble in water, but its solubility is much lower than that of ammonia. At room temperature, CO₂ has a solubility of about 0.2 g per 100 mL of water. While it does dissolve to some extent, it does not reach the high levels of solubility that ammonia does. Additionally, CO₂ reacts with water to form carbonic acid (H₂CO₃), which can complicate its solubility behavior. 4. **Chlorine (Cl₂)**: - Chlorine is a nonpolar molecule and is less soluble in water compared to ammonia. Its solubility is limited due to the lack of strong interactions with water molecules. Chlorine does dissolve in water, but only to a small extent (approximately 0.7 g per 100 mL at room temperature). Moreover, chlorine can react with water to form hydrochloric acid (HCl) and hypochlorous acid (HClO), which can further affect its solubility. 5. **Nitrogen (N₂)**: - Nitrogen is a diatomic, nonpolar gas and is very poorly soluble in water. Its solubility is about 0.018 g per 100 mL at room temperature. The nonpolar nature of nitrogen means it does not interact favorably with polar water molecules, leading to its low solubility. ### Summary of Why Other Options Are Incorrect: - **B. Carbon (IV) oxide (CO₂)**: While it is soluble, its solubility is significantly lower than that of ammonia. - **C. Chlorine (Cl₂)**: It has low solubility due to its nonpolar nature and limited interaction with water. - **D. Nitrogen (N₂)**: It is very poorly soluble in water due to its nonpolar characteristics. ### Revision Summary: - Ammonia (NH₃) is highly soluble in water due to its polar nature and ability to form hydrogen bonds. - Carbon dioxide (CO₂) has lower solubility and reacts with water, forming carbonic acid. - Chlorine (Cl₂) is less soluble due to its nonpolar nature and limited interaction with water. - Nitrogen (N₂) is poorly soluble in water because it is a nonpolar gas. Understanding the solubility of gases in water is crucial for various applications in chemistry, including environmental science and industrial processes.