Statement I: The solubility of a gas in a liquid increases with increase of pressure.
Statement II: The solubility of a gas in a liquid, expressed as the mole fraction of the gas in the solution at equilibrium, is directly proportional to the partial pressure of the gas.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I.
Henry’s law relates the solubility of a gas in a liquid to the pressure of that gas above the liquid.
Statement I: The solubility of a gas in a liquid increases with increase of pressure. — True. Compressing the gas over the solution puts more gas particles in each unit volume, so more of them strike the surface and enter the liquid; the gas dissolves until a new equilibrium is reached at a higher solubility.
Statement II: The solubility of a gas in a liquid, expressed as the mole fraction of the gas in the solution at equilibrium, is directly proportional to the partial pressure of the gas. — True. This is Henry’s law in its mole-fraction form, \( p=K_\mathrm{H}\,x \).
Why Statement II explains Statement I? Since x = p/KH and KH is constant at a given temperature, a rise in the partial pressure p raises the mole fraction x of the dissolved gas. That proportionality is the reason the solubility increases with pressure.
NCERT (2026-27 edition):
1.3.2 Solubility of a Gas in a Liquid – “… Solubility of gases in liquids is greatly affected by pressure and temperature. The solubility of gases increase with increase of pressure.”
“… If we use the mole fraction of a gas in the solution as a measure of its solubility, then it can be said that the mole fraction of gas in the solution is proportional to the partial pressure of the gas over the solution.”