Which of the following statements is true of the critical temperature of a pure substance?
a. the critical temperature is the temperature above which the liquid phase of a pure substance can exist.
b. the critical temperature is the temperature above which the liquid phase of a pure substance cannot exist.
c. the critical temperature is the temperature below which the liquid phase of a pure substance cannot exist.
d. the critical temperature is the temperature at which all three phases can coexist.
e. the critical temperature is the temperature at which the pure substance reaches, but cannot go beyond, the critical pressure.
can someone explain this one?