18 g glucose (C₆H₁₂O₆) is added to 178.2 g water. The vapour pressure of water (in torr) for this aqueous solution is:

The molar masses of glucose and water are 180g/mol and 18g/mol respectively. Number of moles of glucose 18 0.1 180 Number of moles of water 178.2 9.9 18 Mole fraction of glucose 0.1 0.01 0.1 9.9 Relative lowering in vapour pressure is equal to the mole fraction of glucose, 1 1 1 760 0.01 760 760 7.6 760 7.6 752.4 solute total n P P n P P P torr Hence, option (b) is correct.