(D) Liquid is being formed.
Step-by-step explanation:
The enthalpy of fusion of a substance (–Hfus) is the change in its enthalpy when the substance changes its state from a solid to a liquid. It happens when heat is supplied to some quantity of substance which is originally in solid state & it turns into liquid.
Example- melting of ice.
To melt ice energy is required. Approximately, 333 kJ of energy is needed to heat 1 kg ice to convert into liquid.