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Question:

The mole fraction of a solvent in an aqueous solution of a solute is 0.8. The molality (in mol kg⁻¹) of the aqueous solution is:

13.88

13.88 × 10⁻²

13.88 × 10⁻¹

13.88 × 10⁻³

Solution:

Correct option is C.
Xsolvent = 0.8
If nT = 1
nsolvent = 0.8
nsolute = 0.2
molality = 0.2 / (0.8 × 18 × 1000) = 13.88