A solution containing 10 g per dm³ of urea (molecular mass = 60 g mol^$$-$$1) is isotonic with a 5% solution of a nonvolatile solute is

1.00 g of a non-electrolyte solute (molar mass 250 g mol^$$-$$1) was dissolved in 51.2 g of benzene. If the freezing point depression constant, K_f of benzene is 5.12 K kg mol^$$-$$1, the freezing point of benzene will be lowered by

A solution of urea (mol. mass 56 g mol^$$-$$1) boils at 100.18^oC at the atmospheric pressure. If K_f and K_b for water are 1.86 and 0.512 K kg mol^$$-$$1 respectively, the above solution will freeze at

A solution has a 1 : 4 mole ratio of pentane to hexane. The vapour pressures of the pure hydrocarbons at 20^oC are 440 mm Hg for pentane and 120 mm Hg for hexane. The mole fraction of pentane in the vapour phase would be