Which statement best explains mass during a phase change from liquid to solid (e.g., water freezing)?

• A. Mass remains the same
• B. Mass increases
• C. Mass decreases
• D. Mass is created

Answer: (A)

In a phase change from liquid to solid, the amount of matter doesn't change. The same number of molecules are present before and after freezing; they just rearrange and release or absorb latent heat as they move into a solid structure. Because mass is about how much matter there is, not how orderly the molecules are, mass stays constant during freezing. The fact that ice expands and becomes less dense than liquid water shows volume and density can change without changing total mass.

That’s why the statement mass remains the same is the best answer. The other possibilities imply adding, removing, or creating matter, which doesn’t happen in a simple phase change.