If 8 g of a non - electrolyte solute is dissolved in 114 g of n-octane to reduce its vapour pressure to 80%, the molar mass (in g mol -1 ) of the solute is
[Given that molar mass of n-octane is ]
60
80
20
40
We know that,
Relative lowering of vapour pressure = Mole fraction of solute
Assuming that the solution is very dilute
i.e.
We have,
Hence, the correct answer is option 4.
Note : NTA's assumption of very dilute solution is although not correct, but no other option can be arrived at by not neglecting with respect to
.