Correction to problem 6d on PS6

It turns out that neither bottle can be frozen the way mentioned. Here is a new problem statement for 6d:

An alternative way to freeze the solutions is to change the pressure. At 0 °C for each bottle, what pressure must be reached in order for freezing to begin? Assume the water freezes first, and assume constant molar densities. Why are these numbers unrealistic? What is special about water freezing here, relative to other liquids?