Final answer:
Lewin's three-step model includes unfreezing, change, and refreezing. Phase changes to a more energetic state include melting (solid to liquid) and vaporization (liquid to gas), which both require heat energy to occur.
Step-by-step explanation:
The student's question about Lewin's three-step model and phase changes both pertain to the concepts within physical science. The correct answer to fill in the blank for Lewin's three-step model is a. Refreezing. The three steps of Lewin's model are: unfreezing, change, and refreezing.
Regarding the phase changes where matter undergoes a transition to a more energetic state, the correct answer is c. melting and vaporization. When a substance melts, it transitions from a solid to a liquid, and during vaporization, it transitions from a liquid to a gas. Both processes require the input of energy, typically in the form of heat, to overcome the intermolecular attractions in the solid or liquid phase which allows the molecules to move more freely, thus entering a more energetic state.