Calculate mole fraction of HCl containing 24.8% of HCl by mass.

HCl is 24.8% by mass solution..... ie. 24.8 g HCl in 100 g of water.
So, mass of HCl= 24.8g and mass of water = 100-24.8 = 75.2 g.
 Molar masses are -   HCl = 36.5 g/mol  ans water - 18 g/mol
Therefore, no. of  moles of HCl = ( mass of HCl ) /  molar mass of HCl = 24.8/36.5 =  0.68 moles
                  no. of  moles of water = ( mass of water ) / molar mass of water = 75.2 / 18 = 4.18 moles
Hence mole fraction of HCl =  (no. of moles of HCl ) / total no.of moles of HCl and water
                                              =  (0.68) / (0.68+4.18) = (0.68) / (4.86)
                                             =  0.139
Hence , mole fraction of HCl in the given solution is 0.139.