Hello!
The answer is: Sublimation.
Why?
From the model, we have that the phase transition type is sublimation since there is a substance in the solid phase changed to the gas phase.
Sublimation is the process where a substance changes its phase (state) from solid to gas phase without passing through the liquid phase.
When the molecules of a substance are joined, meaning that the space between them is minimum, it's called a solid phase.
When the molecules of a substance are separated, even more than they are in the liquid phase, there is a new phase called the gas phase.
Have a nice day!
