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Chemistry · Solutions and Colligative Properties

JEE Main 2025 — 7 April, Evening Shift — Question 9

Liquid AA and BB form an ideal solution. The vapour pressures of pure liquids AA and BB are 350 and 750 mm Hg respectively at the same temperature. If XAX_{A} and XBX_{B} are the mole fraction of AA and BB in solution while yAy_{A} and yBy_{B} are the mole fraction of AA and BB in vapour phase then,

  1. Option A:

    xAxB=yAyB\frac{x_{A}}{x_{B}}=\frac{y_{A}}{y_{B}}

  2. Option B:

    xAxB<yAyB\frac{x_{A}}{x_{B}}<\frac{y_{A}}{y_{B}}

  3. Option C:

    xAxB>yAyB\frac{x_{A}}{x_{B}}>\frac{y_{A}}{y_{B}}

    Correct
  4. Option D:

    (xA−yA)<(xB−yB)\left(x_{A}-y_{A}\right)<\left(x_{B}-y_{B}\right)

Answer: C

Step-by-step solution

PA0=350 mmHgP_{A}^{0}=350 \mathrm{~mm} \mathrm{Hg}

PB0=750 mmHgP_{B}^{0}=750 \mathrm{~mm} \mathrm{Hg}

yA=350xAPTyB=350xBPTyAyB=350xA750xB⇒yAyB<xAxB\begin{aligned} & y_{A}=\frac{350 x_{A}}{P_{T}} \quad y_{B}=\frac{350 x_{B}}{P_{T}} \\& \frac{y_{A}}{y_{B}}=\frac{350 x_{A}}{750 x_{B}} \\& \Rightarrow \frac{y_{A}}{y_{B}}<\frac{x_{A}}{x_{B}} \end{aligned}

Answer key and solution verified before publishing.

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Exam
JEE Main 2025
Paper
7 April, Evening Shift
Subject
Chemistry
Chapter
Solutions and Colligative Properties
Topic
Liquid in Liquid Solutions (Raoult's Law)

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