Question

Given below are two statements. Assertion (A): Molar solubility of a gas in a liquid decreases with increase in pressure at constant temperature. Reason (R): Henry's law describes that at constant temperature, the partial pressure of a gas in vapour phase is directly proportional to the mole fraction of the gas in solution. Choose the most appropriate answer.

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

According to Henry's law, gas solubility in liquid increases with increase in pressure at constant temperature.

Answer 1

The Correct Option is D

Step 1: Understand Henry's law.
Henry's law states: \[ p=K_Hx \] where: \[ p=\text{partial pressure of gas} \] \[ x=\text{mole fraction of gas in solution} \] \[ K_H=\text{Henry's law constant} \]

Step 2: Meaning of Henry's law.
At constant temperature: \[ p\propto x \] This means that if pressure of gas increases, the amount of gas dissolved in liquid also increases.

Step 3: Check Assertion (A).
Assertion says that molar solubility of gas decreases with increase in pressure. This is wrong. Actually: \[ \text{Solubility of gas increases with increase in pressure}. \] So Assertion (A) is not correct.

Step 4: Check Reason (R).
Reason says that partial pressure of gas is directly proportional to mole fraction of gas in solution. This is exactly Henry's law. So Reason (R) is correct.

Step 5: Final answer.
Therefore: \[ \text{(A) is not correct but (R) is correct}. \]