Answer
Please see the work below.
Work Step by Step
We know that
a. When $I_2$ vapor is cooled at $120$atm no change to a distinct liquid will be observed but $I_2$ will condense to a solid phase at some specific temperature.
b. When $I_2$ is cooled at 1atm, the vapor will condense to a liquid and then freeze to the solid phase.
c. When $I_2$ vapor is cooled at $50mm Hg$, the vapor will condense directly to the solid phase without going through the liquid phase.
