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 ?
MHT CET
Chemistry
Solutions
2026
MHT CET 2026 (16 April Shift 1)
MHT CET Chemistry Question (2026) — Solution
Options
- A. 0.02
- B. 0.08
- C. 0.2
- D. 0.8
Answer
D. 0.8
Step-by-step solution
Let the vapour pressure of the pure solvent be P^0. The decrease in vapour pressure is given as 20\%, so the lowering of vapour pressure is P = 0.20 P^0. According to Raoult's law, the relative lowering of vapour pressure is equal to the mole fraction of the solute, X_ solute . P P^0 = X_ solute X_ solute = 0.20 P^0 P^0 = 0.20 For a binary solution, the sum of mole fractions of solute and solvent is 1. X_ solvent = 1 - X_ solute X_ solvent = 1 - 0.20 = 0.8 Answer: 0.8
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