Final answer:
Point B on the phase diagram represents the normal melting point, where a solid becomes liquid, making B) melting the correct answer to the phase change at point B.
Step-by-step explanation:
Based on the phase diagram provided, point B on the phase diagram represents the normal melting point of a substance. At this point, the solid phase of a substance transitions to the liquid phase at a constant temperature and pressure. The term melting describes this specific phase change, so the correct answer to the student's original question is B) melting. During melting, matter undergoes a transition to a more energetic state as the particles gain energy, move apart from their fixed positions, and begin to move more freely. Option B) melting and sublimation would be the phase changes where matter transitions to a more energetic state.