In which situation would you expect a gas to remain in solution only until saturation is reached?

The scenario where a gas remains in solution only until saturation is reached is closely tied to the principles of gas solubility and Henry's Law, which states that the amount of gas that will dissolve in a liquid at a given temperature is directly proportional to the partial pressure of that gas above the liquid.

When you raise the pressure of a gas above a liquid, you effectively increase the amount of that gas that can dissolve in the liquid. However, once the system reaches saturation, no more gas can dissolve despite the increased pressure, and any additional gas would remain in the gaseous phase rather than dissolving into the liquid. This dynamic illustrates how solubility is contingent upon the balance of pressure and the specific gas's properties.

In contrast, breathing at surface level does not involve a pressure change significant enough to affect gas solubility in the way described. Cooling the liquid can change gas solubility, often increasing it, thus allowing more gas to remain in solution. Reducing the amount of gas in the liquid does not dictate how it remains in solution; rather, it alters the concentration without directly addressing saturation limits. Therefore, raising the pressure is the situation that directly leads to the described conditions of gas solubility reaching saturation.