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NEET Chemistry QUESTION #1091
Question 1
5 moles of liquid X and 10 moles of liquid Y form a solution with vapour pressure 70 torr. Pure X: 63 torr, pure Y: 78 torr. What is true about the solution?
  • The solution is ideal
  • The solution has volume greater than sum of individual volumes
  • The solution shows positive deviation
  • The solution shows negative deviation✔️
Correct Answer Explanation
Ideal vapour pressure by Raoult's law: \(P_{ideal}=x_X P_X^* + x_Y P_Y^* = \frac{5}{15}\times63+\frac{10}{15}\times78=21+52=73\ \text{torr}\). Observed pressure = 70 torr \(<\) 73 torr (ideal). Since observed \(<\) ideal, the solution shows negative deviation from Raoult's law.