Final answer:
The phase change of molten lava into solid rock is freezing or solidification, an exothermic process that releases energy as heat.
Step-by-step explanation:
When molten lava from a volcano turns into solid rock, the phase change that occurs is known as solidification or freezing. During this process, energy is released, not required, because the transition is from a less ordered state (liquid) to a more ordered state (solid), which allows intermolecular forces to re-establish themselves and release energy in the form of heat. Therefore, the correct answer is (b) Freezing - Requires energy. However, this description doesn't match the phase change presented in the question since it's a common misunderstanding that freezing requires energy due to the phrasing. The truth is that freezing releases energy, so the correction would be (b) Freezing - Releases energy.