The correct option is **B. The pressure of the gas 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. This solubility is influenced by several factors, but one of the most significant is the pressure of the gas above the liquid. 2. **Henry's Law**: The relationship between the solubility of a gas and the pressure of that gas 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 the solubility. Conversely, if the pressure decreases, the solubility of the gas in the liquid also decreases. This principle 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 Other Options Are Incorrect: - **A. The size of the gas molecules**: While the size of gas molecules can influence how easily they can move through the liquid, it is not the primary factor affecting solubility. Smaller gas molecules may diffuse more easily, but solubility is more directly related to pressure and temperature. - **C. The color of the gas**: The color of a gas has no bearing on its solubility in a liquid. Solubility is a physical property related to interactions between gas molecules and the solvent, not their visual characteristics. - **D. The presence of other dissolved substances**: While the presence of other dissolved substances can affect the solubility of a gas (for example, through changes in the solvent's properties), it is not the primary factor. The effect of pressure on gas solubility is much more significant and direct. ### Common Pitfalls: - **Confusing solubility with diffusion**: It's important to distinguish between solubility (how much gas can dissolve) and diffusion (how gas molecules move through a liquid). Increased pressure directly affects solubility, while diffusion is influenced by concentration gradients and temperature. - **Ignoring temperature**: While the question specifies constant temperature, it's crucial to remember that temperature also plays a significant role in gas solubility. Generally, as temperature increases, gas solubility decreases. ### Revision Summary: - The solubility of a gas in a liquid is primarily affected by the pressure of the gas above the liquid. - Henry's Law describes the direct relationship between gas pressure and solubility. - Other factors like molecular size, color, and the presence of other substances have less impact compared to pressure. - Always consider the effects of temperature when discussing gas solubility, even if it is held constant in a specific question.