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JEE Mains · Chemistry · STD 12 -1. Solution and colligative properties

At \(20^{\circ} \mathrm{C}\), the vapour pressure of benzene is \(70 \,torr\) and that of methyl benzene is \(20\, torr.\) The mole fraction of benzene in the vapor phase at \(20^{\circ} \mathrm{C}\) above an equimolar mixture of benzene and methyl benzene is \(.....\,\times 10^{-2}\) (Nearest integer)

  1. A \(71\)
  2. B \(87\)
  3. C \(95\)
  4. D \(78\)
Verified Solution

Answer & Solution

Correct Answer

(D) \(78\)

Step-by-step Solution

Detailed explanation

\(P_{B}^{\circ}=70 \quad P_{T}^{0}=20 \quad X_{B}=0.5=X_{M}\) Now. \(y_{B}=\frac{X_{B} P_{B}^{\circ}}{X_{B} P_{B}^{\circ}+X_{M} P_{M}^{0}}\) \(=\frac{70 \times 0.5}{70 \times 0.5+20 \times 0.5}\) \(=0.777 \Rightarrow 77.7 \times 10^{-2} \Rightarrow 78 \times 10^{-2}\)
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