Final answer:
The iodine crystals disappearing from an evaporating dish demonstrate sublimation, which is an endothermic process as it requires the absorption of energy.
Step-by-step explanation:
The disappearance of crystals of iodine from an evaporating dish as they stand in the fume hood is an example of a phase change known as sublimation. During sublimation, a substance changes from a solid state directly to a gaseous state without passing through the liquid state.
This phase change is an endothermic process, meaning it requires energy to occur. The correct answer to the student's question is: a) Sublimation - Requires energy. Substances that undergo sublimation absorb energy to overcome the intermolecular forces holding the solid together, thereby transitioning directly into the gas phase.