Fact 1: Phase changes do not change mass.

Fact 2: Particles have mass, but mass is energy.

Given the two facts above, answer the question "What property of matter is not changed during a phase change?" with the following options: 
- motility
 - sweating
 - energy
 - cold
 - nucleus
 - density
 - apoptosis
 - an object


 

   energy      