We Wish to Lower the Freezing Point of the Water

Multiple Choice

We wish to lower the freezing point of the water in an automobile radiator to -40 °C.The total mass of water present is 12.0 kg.For which one of the following compounds would we have to use the greatest mass of solute to achieve this? You may assume that K_f for water = -1.86 °C/m and that all ionizable solutes are completely ionized with unit activity even at this high concentration.

A) AlF₃ (M.W.= 84 g/mol)
B) C₂H₅OH (M.W.= 46 g/mol)
C) CaCl₂ (M.W.= 111 g/mol)
D) C₃H₆(OH) ₂ (M.W.= 76 g/mol)
E) NaCl (M.W.= 58.5 g/mol)