Option A is correct: mole fraction and mass percent (w/w) are both unitless. Mole fraction xi=‌
ni
Σjnj
It's simply a ratio of moles, so no units. Mass percent (w/w) ‌ mass ‌1%=‌
‌ mass of solute ‌
‌ total mass of solution ‌
×100% Again, a ratio of masses, giving a percentage without units. By contrast, molality has units of mol/kg and molarity has mol/L, so neither is unitless.