Answer:
The solutions are listed from the lowest freezing point to highest freezing point. 
 Mg₃(PO₄)₂ -  AlBr₃ - BeBr₂ -  KBr
Explanation:
Colligative property of freezing point, is the freezing point depression.
Formula is:
ΔT = Kf . m . i
Where ΔT = T° freezing pure solvent - T° freezing solution 
Kf is the cryoscopic constant
m is molality and i is the Van't Hoff factor (number of ions, dissolved in solution)
In this case, T° freezing pure solvent is 0° because it's water, so the Kf is 1.86 °C/m, and m is 0.1 molal.
The i modifies the T° freezing solution. The four salts, are ionic compounds, so for each case:
BeBr₂  → Be²⁺  +  2Br⁻   i = 3
AlBr₃ →  Al³⁺  + 3Br⁻   i = 4
Mg₃(PO₄)₂  →  3Mg²⁺  +  2PO₄⁻³    i = 5
KBr →  K⁺  +  Br⁻   i = 2
Solution of Mg₃(PO₄)₂ will have the lowest temperature of freezing and the solution of KBr, the highest (always lower, than 0°).