What is the mole fraction of lif in an aqueous solution that contains 39.4% lif (weight/weight %) ?

The solution contains 39.4% of LiF. Assume that the solution is 100ml. The molar mass of LiF is 25.939, the amount of LiF in mole would be: 100ml * 1g/ml * 39.4% / 25.939g/mol = 1.52 mol LiF

Then the mass of the water would be: 100gram - 39.4g = 60.6g

If the molar mass of water is 18.015 the mole of the water would be: 60.6g / 18.015g/mol = 3.36 mol

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The mole fraction would be:1.52 mol / 1.52+3.36 = 0.339