1. Calculate the molality of the solution.

* Molar mass of biphenyl (C12H10): 12(12.01 g/mol) + 10(1.01 g/mol) = 154.21 g/mol

* Moles of biphenyl: 0.771 g / 154.21 g/mol = 0.005 mol

* Molality (m): moles of solute / kg of solvent = 0.005 mol / 0.025 kg = 0.2 mol/kg

2. Calculate the freezing point depression.

* Freezing point depression constant (Kf) for cyclohexane: 20.0 °C/m

* Freezing point depression (ΔTf): Kf * molality = 20.0 °C/m * 0.2 mol/kg = 4.0 °C

3. Calculate the freezing point of the solution.

* Normal freezing point of cyclohexane: 6.5 °C

* Freezing point of the solution: 6.5 °C - 4.0 °C = 2.5 °C

Therefore, the freezing point of the solution is 2.5 °C.