Q. The vapour pressure of pure liquid is 1.2 atm. When a non-volatile substance B is mixed in A, then its vapour pressure becomes 0.6 atm. The mole fraction of B in the solution is
A) 0.15
B) 0.25
C) 0.50
D) 0.75
Explanation
(c)
According to Raoult’s law
$\frac{p - p_{s}}{p} = X_{B}$ (mole fraction of solute)
$X_{B} = \frac{1.2 - 0.6}{1.2} = \frac{0.6}{1.2}$
=0.5
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.