Looks like it's D..
We know water normally has a freezing/melting point of 0. So, if it is now -0.46 then we need to determine which substrate would give this.
The formula to use is deltaT=k*b*i
deltaT is 0.46 in this example as stated above. i is the number of ion particles, and b is the molality.
In this case we have 10 g/1kg of solvent (water). If you use CaCl2 then the molar mass is ~110 g/mole which means we have about 0.09 moles/kg of water. (10/110 = 0.09)
Since there are 3 ion particle in CaCl2 we see that the product of 0.09 * 3 * 1.86 (constant in the formula)= ~0.5 which is close to the 0.46 celsius change. This answer gave me the closest value.
Hope that matches up with the answer in the book.. I take it this is from EK? There may be a non-mathematical way of doing this, but this is the way I worked it out.