What happens when the volume of a gas is compressed underwater?

When the volume of a gas is compressed underwater, the gas molecules are forced closer together due to the increased pressure. According to Boyle's Law, which states that the volume of a gas is inversely proportional to its pressure (when temperature remains constant), as pressure increases, the volume must decrease.

Underwater, the ambient pressure is significantly higher than at the surface, causing any gas contained within a sealed environment (like a diver's lungs or a buoyancy control device) to have a reduced volume. This principle is fundamental for divers to understand, as it affects buoyancy and the handling of gases in diving equipment.

In contrast, the other options do not align with the principles of physics governing gases. The volume does not remain constant under increased pressure, nor does it increase, which would contradict Boyle's Law. Additionally, gas evaporation is not relevant in this context, as that pertains more to liquids transitioning to gas rather than gas volume changes under pressure.