Challenge Your Exam Readiness With Our Free MCAS Practice Questions

MCAS STE standards emphasize conservation of matter and energy, phase changes, and system boundaries. In a closed, insulated container, no matter enters or leaves. Melting is a phase change from solid to liquid at constant mass; the number of water molecules remains the same. Although melting is endothermic (absorbs energy), energy transfer does not change the mass of the water in a classical measurement scenario (ignoring relativistic effects). Therefore, A is incorrect: absorbing heat does not remove matter. Option C confuses density with mass. While liquid water is denser than ice (ice floats due to lower density), density relates mass to volume; changing phase alters volume, not the total mass. Option D suggests random measurement variability, but with a proper scale and closed container, mass remains constant. The correct answer is B: mass is conserved. MCAS often asks students to apply conservation principles and distinguish between open and closed systems. The key scientific practice is defining system boundaries and recognizing that phase changes rearrange particles’ positions and energy without creating or destroying matter.