Answer:
The solutions are listed from the lowest freezing point to highest freezing point.
Mg₃(PO₄)₂ - AlBr₃ - BeBr₂ - KBr
Step-by-step 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°).