Answer:
L
Explanation:
The details tell us that the substance starts out and its atoms are "close together and cannot slide past one another." This describes a solid: liquids and gases' atoms can move freely, but solids' atoms cannot move. So we know that the substance starts as a solid.
That means the answer must be L or P, because the solid needs to change into something else.
Then the substance gains energy and it can fill its container. Well, this could be either gas or liquid! So it's a good thing that only L is an answer choice, because that means L is correct and the change is from solid -> gas.
