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1. Solution and colligative properties — Chemistry STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 ScienceChemistry1. Solution and colligative properties1 Mark
MCQ
Assertion : If a liquid solute more volatile than the solvent is added to the solvent, the vapour pressure of the solution may increase i.e., $p_s > p^o$.

Reason : In the presence of a more volatile liquid solute, only the solute will form the vapours and solvent will not.

  • ✓
    If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
  • B
    If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
  • C
    If the Assertion is correct but Reason is incorrect.
  • D
    If both the Assertion and Reason are incorrect.
✓

Answer

Correct option: A.
If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
a
Given $P _{ A }^{0}=21\, kPa \quad \Rightarrow P _{ B }^{0}=18\, kPa$

$\rightarrow$ An Ideal solution is prepared by mixing $1\, mol$ $A$ and $2 \,mol\, B$.

$\rightarrow X_{A}=\frac{1}{3}$ and $X_{B}=\frac{2}{3}$

$\rightarrow$ Acc to Raoult's low

$P _{ T }= X _{ A } P _{ A }^{0}+ X _{ B } P _{ B }^{0}$

$P _{ T }=\left(\frac{1}{3} \times 21\right)+\left(\frac{2}{3} \times 18\right)$

$P _{ T }=7+12=19\, KPa$

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