**Correct Option: B. The pressure of the gas above the liquid** ### Detailed Explanation: To understand why the pressure of the gas above the liquid primarily affects the solubility of a gas in a liquid, we can refer to 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. The mathematical expression of Henry's Law is: \[ C = k_H \cdot P \] Where: - \( C \) is the concentration of the dissolved gas in the liquid (usually in mol/L). - \( k_H \) is Henry's Law constant (which varies for different gases and solvents). - \( P \) is the partial pressure of the gas above the liquid. #### Step-by-Step Explanation: 1. **Understanding Gas Solubility**: When a gas is in contact with a liquid, some of the gas molecules collide with the liquid surface and can enter the liquid phase. The rate at which this happens depends on how many gas molecules are present above the liquid, which is influenced by the pressure of the gas. 2. **Effect of Pressure**: Increasing the pressure of the gas above the liquid increases the number of gas molecules that collide with the liquid surface. This leads to a higher rate of gas molecules entering the liquid, thus increasing solubility. Conversely, if the pressure decreases, fewer gas molecules are available to dissolve, leading to lower solubility. 3. **Real-World Example**: A practical example of this is carbonated beverages. When the bottle is sealed, the pressure of carbon dioxide (CO₂) gas above the liquid is high, allowing a significant amount of CO₂ to dissolve in the liquid. When the bottle is opened, the pressure drops, and the gas escapes, leading to the fizzing sound and the loss of carbonation as CO₂ comes out of solution. ### Why Other Options Are Incorrect: - **A. The size of the gas molecules**: While the size of gas molecules can influence diffusion rates and the speed at which they can enter a liquid, it does not primarily determine solubility. Smaller gas molecules may diffuse faster, but solubility is more directly related to pressure and the nature of the gas and solvent. - **C. The color of the liquid**: The color of the liquid has no impact on the solubility of a gas. Solubility is a chemical property that depends on interactions at the molecular level, such as polarity and intermolecular forces, rather than visual characteristics like color. - **D. The presence of other solutes in the liquid**: While the presence of other solutes can affect the overall solubility of a gas (due to changes in solvent properties or competition for solvation), it is not the primary factor. The effect of pressure on gas solubility is much more significant and direct. ### Summary of Key Points: - **Henry's Law**: The solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. - **Pressure Impact**: Increasing pressure increases the number of gas molecules that can dissolve in the liquid. - **Real-World Application**: Carbonated drinks illustrate the effect of pressure on gas solubility. - **Other Factors**: Size of gas molecules, color of the liquid, and presence of other solutes are less significant compared to pressure. This understanding of gas solubility is crucial for various applications in chemistry, environmental science, and engineering, particularly in processes involving gases and liquids.