Colligative properties: Freezing point depression.
The depression in freezing point will depend on the total number of particles present, and the molality of those particles. We are given the molarity (not molality) of the different solutions so we'd really need the density of these solutions to compute molality. But assuming the values won't differ too much from molarity, we'll proceed as follows:
a. 0.10 M lithium chloride: 2 particles x 0.1 = 0.2
b. 0.15 M barium nitrate: 3 particles x 0.15 = 0.45
c. 0.20 M potassium iodide: 2 particles x 0.2 = 0.4
d. 0.25 M sodium nitrate: 2 particles x 0.25 = 0.5
e. 0.20 M calcium bromide: 3 particles x 0.20 = 0.60 which is the highest value so it would have the greatest effect on the freezing point.