The correct option is **C. Pressure above the liquid**. ### Detailed Explanation: 1. **Understanding Gas Solubility**: The solubility of a gas in a liquid refers to the amount of gas that can dissolve in a given volume of liquid at a specific temperature and pressure. This phenomenon is influenced by several factors, but the most significant one is the pressure of the gas above the liquid. 2. **Henry's Law**: The relationship between the solubility of a gas and the pressure above the liquid is described by Henry's Law. Henry's Law states that at a constant temperature, the amount of gas that dissolves in a liquid is directly proportional to the partial pressure of that gas above the liquid. Mathematically, it can be expressed as: \[ C = k_H \cdot P \] where: - \( C \) is the concentration of the dissolved gas, - \( k_H \) is Henry's Law constant (specific to each gas-liquid combination), - \( P \) is the partial pressure of the gas. 3. **Effect of Pressure**: When the pressure of the gas above the liquid increases, more gas molecules are forced into the liquid, increasing its solubility. Conversely, if the pressure decreases, the solubility of the gas also decreases. This is why carbonated beverages are bottled under high pressure; when the bottle is opened, the pressure drops, and the gas escapes, leading to fizz. ### Why the Other Options Are Incorrect: - **A. Temperature of the liquid**: While temperature does affect the solubility of gases, it is not the primary factor. Generally, as temperature increases, the solubility of gases in liquids decreases because gas molecules gain kinetic energy and escape from the liquid more easily. However, this effect is secondary to the influence of pressure. - **B. Surface area of the gas**: The surface area of the gas does not significantly affect its solubility in a liquid. While a larger surface area can increase the rate of gas transfer into the liquid, it does not change the equilibrium solubility of the gas. The solubility is determined by the pressure and temperature, not the surface area. - **D. Color of the gas**: The color of the gas has no impact on its solubility in a liquid. Solubility is a physical property that depends on molecular interactions and does not relate to the visual characteristics of the gas. ### Common Pitfalls: - **Confusing solubility with rate of dissolution**: It's important to distinguish between how quickly a gas dissolves in a liquid (rate) and how much can dissolve (solubility). Pressure affects solubility, while surface area and agitation can affect the rate of dissolution. - **Ignoring temperature effects**: While temperature does play a role, it is often misunderstood as being the primary factor affecting gas solubility. Remember that pressure is the dominant factor. ### Revision Summary: - The primary factor affecting the solubility of a gas in a liquid is the **pressure above the liquid** (Henry's Law). - Increasing pressure increases gas solubility, while decreasing pressure reduces it. - Temperature affects gas solubility but is secondary to pressure. - Surface area and color of the gas do not significantly influence solubility.