Explain why the roller coaster’s potential energy is greater at point 1 than at point 4.

Point 1 is PROBABLY higher up than point 4.

Another possibility is that on the way from Point 1 to point 4,
a lot of people are falling out of the coaster.

We have no way to tell, because you neglected to show us
the picture that goes with this question.  It's important. 

Sublimation- which change of state is shown in model