What is the heat of fusion?

Heat of fusion is defined as the amount of energy required to change a substance from solid to liquid at its melting point, without any change in temperature. This process involves breaking the intermolecular forces that hold the solid structure together. Since the temperature remains constant during this phase transition, the energy input is entirely used for changing the state of the material rather than increasing its temperature.

In the context of this question, the correct answer accurately captures this concept by specifying that it is the energy needed to convert one gram of a solid into a liquid at its melting point without any change in temperature. Understanding the heat of fusion is essential for comprehending how different materials behave when heated and how phase transitions occur in various physical processes.