Henry was the first to give a quantitative relation between pressure and solubility of a gas in a solvent. Choose the correct statement given by Henry.

The partial pressure of the gas in vapour phase is proportional to the mole fraction of the gas in the solution.

The correct answer is Option (2) → The partial pressure of the gas in vapour phase is proportional to the mole fraction of the gas in the solution.

Henry’s Law states that at constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the solution.

Mathematically, Henry’s law is expressed as:

p = KH × x

Where

p = partial pressure of the gas in vapour phase

x = mole fraction of the gas in the solution

KH = Henry’s law constant

This equation shows that partial pressure is directly proportional to the mole fraction of the gas dissolved in the liquid.

Therefore, when the pressure of the gas increases, its solubility in the liquid also increases.

Henry’s law is applicable mainly to gases that do not chemically react with the solvent.

Option-wise Explanation

Option 1: The partial pressure of the gas in vapour phase is inversely proportional to the mole fraction of the gas in the solution.

Incorrect. According to Henry’s law, the relation is directly proportional, not inversely proportional.

Option 2: The partial pressure of the gas in vapour phase is proportional to the mole fraction of the gas in the solution.

Correct. This statement directly represents Henry’s law equation (p = KH x).

Option 3: The total pressure of the gases in vapour phase is proportional to the multiplication of the mole fraction of all the gases present in the solution.

Incorrect. This statement does not represent Henry’s law and has no physical meaning in this context.

Option 4: The total pressure of the gases in vapour phase is proportional to the sum of the mole fraction of all the gases present in the solution.

Incorrect. This idea is related to Dalton’s law of partial pressures, not Henry’s law.