partial pressure = total pressure * mole fraction since partial pressure are equal then P(He) = P(O2) total pressure * mole fraction(He) =total pressure * mole fraction(O2) So mole fraction(He) =mole fraction(O2) Hence they have equal number of moles Solution partial pressure = total pressure * mole fraction since partial pressure are equal then P(He) = P(O2) total pressure * mole fraction(He) =total pressure * mole fraction(O2) So mole fraction(He) =mole fraction(O2) Hence they have equal number of moles.