The solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid; this relation is described by which law?

• A. Boyle's Law
• B. Henry's Law
• C. Dalton's Law
• D. Raoult's Law

Answer: (B)

The main idea being tested is how gas solubility in a liquid relates to the gas’s partial pressure above the liquid. This is described by Henry’s Law: at a given temperature, the amount of dissolved gas is proportional to its partial pressure in contact with the liquid. In equation form, concentration of dissolved gas equals Henry’s constant for the gas–solvent pair times the partial pressure of the gas above the liquid (C = kH × Pgas). This means increasing the partial pressure pushes more gas into solution, while decreasing the pressure allows gas to come out of solution. Temperature also matters: for most gases, higher temperature lowers solubility.

This concept helps explain many real-world situations, like why carbon dioxide stays dissolved in a sealed soda bottle under high pressure and why it fizzles out when the bottle is opened and the pressure drops. It also underlies phenomena in physiology and environmental chemistry, where the partial pressures of gases drive how much is dissolved in liquids such as blood or water.

The other listed laws don’t describe this relationship. Boyle’s Law deals with how a gas’s volume changes with pressure at constant temperature; Dalton’s Law deals with the sum of partial pressures in a gas mixture; Raoult’s Law deals with how the vapor pressure of a solution changes with composition.