A) 3.2
B) 2
C) 4
D) 3.6
Correct Answer: A
Solution :
Let molality of solution \[=x\] \[\therefore \] Moles of solute in 1000 g benzene \[=\frac{1000}{78}=12.82\] Mole fraction of solute \[=\frac{x}{x+12.82}\] Given mole fraction of solute\[=0.2\] \[\therefore \] \[0.2=\frac{x}{x+12.82}\] or \[0.2(x+12.82)=x\] or \[0.2\,x+2.564=x\] \[2.564=x-0.2x\] \[x=\frac{2.564}{0.8}=3.2\]
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