Which of the following best describes what occurs when a substance melts?

• A. The substance transitions from the gas phase to the solid phase as its particles lose energy and become fixed.
• B. The substance transitions from the liquid phase to the gas phase as its particles escape into the atmosphere.
• C. The substance transitions from the liquid phase to the solid phase as its particles slow down and arrange into a regular pattern.
• D. The substance transitions from the solid phase to the liquid phase as its particles gain enough energy to overcome their fixed positions.

Answer: (D)

Verified step by step guidance

1. Understand the definition of melting: Melting is the phase transition where a substance changes from the solid phase to the liquid phase.
2. Recall the behavior of particles in different phases: In a solid, particles are closely packed in a fixed, orderly arrangement and vibrate in place; in a liquid, particles have more freedom to move around but remain close together.
3. Recognize that melting occurs when particles in a solid gain enough energy (usually from heat) to overcome the forces holding them in fixed positions, allowing them to move more freely and form a liquid.
4. Note that melting is not a transition from gas to solid, nor from liquid to gas, nor from liquid to solid; these correspond to other phase changes (deposition, vaporization, and freezing, respectively).
5. Therefore, the best description of melting is: the substance transitions from the solid phase to the liquid phase as its particles gain enough energy to overcome their fixed positions.