As O₂(l) Is Cooled at 1 Atm, It Freezes at 54.5

Multiple Choice

As O₂(l) is cooled at 1 atm, it freezes at 54.5 K to form Solid I. At a lower temperature, Solid I rearranges to Solid II, which has a different crystal structure. Thermal measurements show that ΔH for the I → II phase transition is -743.1 J/mol and that ΔS for the same transition is -17.0 J/K mol. At what temperature are Solids I and II in equilibrium?

A) 43.7 K
B) 2.06 K
C) 53.4 K
D) 31.5 K
E) They can never be in equilibrium because they are both solids.