A 33.6% mass concentration is equivalent to 33.6 g of phenol in a 100 g solution. Since the solvent is water, then the mass of water is 100 g - 33.6 g = 66.4 g. Now, we convert the amount knowing that the molar mass of phenol is 94 g/mol and that of water is 18 g/mol.
Moles of Phenol = 33.6 g/94 g/mol = 0.357 moles
Moles of Water = 66.4 g/18 g/mol = 3.69 moles
Mole Fraction of phenol = Moles of Phenol/(Moles of Water + Moles of Phenol)
Mole Fraction of phenol = 0.357/(3.69+0.357) = 0.088
