A mole fraction is equal to the moles of one component divided by the total moles in the solution or mixture. The sum of all mole fraction of each component should equate to one. Therefore, we calculate as follows:
mole fraction HCl = 1 - 0.214 - 0.452 - 0.118 - 0.175 = 0.041
Hope this answers the question. Have a nice day.