Answer: a. The heat of vaporization (Hvap) is greater than the heat of fusion (Hfus) for a substance.
Explanation: The heat of vaporization is the amount of heat required to convert a substance from a liquid to a gas at its boiling point, while the heat of fusion is the amount of heat required to convert a substance from a solid to a liquid at its melting point. In general, the heat of vaporization is higher than the heat of fusion for most substances.