How would the vapor pressure of a solution that contains .5 mol of #CaCl_2# in 1.0 kg of water compare with the vapor pressure of a solution that contains 1.5 mol of glucose in 1.0 kg of water?
Their vapour pressures should be comparable.
Calcium chloride speciates in aqueous solution to give calcium ion and 2 equiv chloride ion. The number of particles in solution should be the same as the number of particles of a non-electrolyte three times its strength.
Your problem was designed to emphasize this colligative principle.