Question

For a binary solution, when a nonvolatile nonelectrolyte solute is dissolved in solvent, the vapour pressure of solvent decreases by 20 % . what is mole fraction of solvent in solution ?

• A. \(0.02\)
• B. \(0.08\)
• C. \(0.2\)
• D. \(0.8\)

Hint:

Relative lowering of vapour pressure equals the mole fraction of solute.

Answer 1

The Correct Option is D

Step 1: Raoult's law:
$p = x_1 p^0$ for a nonvolatile solute, where $x_1$ is the solvent mole fraction.

Step 2: Use the data:
The vapour pressure falls by 20 percent, so $p = 0.8\,p^0$.

Step 3: Result:
Then $x_1 = p/p^0 = 0.8$, option (D).

Final Answer:
Solvent mole fraction is 0.8. \[ \boxed{\text{(D) }0.8} \]