Which phase change is an example of an exothermic process?

Answer: Option D

Processes that require or give off heat will be limited to changes of state, known as phase changes, and changes in chemical constitution, or chemical reactions. Changes of state involve a solid melting, a liquid freezing, a liquid boiling or a gas condensing.
An exothermic process is one that gives off heat, which is transferred to the surroundings. An endothermic process is a reaction which heat has to be supplied to the system from the surroundings.
Here in all the given options, heat is taken away from them to change there phase.
Liquid to Solid --- Freezing
Gas to Liquid --- Condensation
Gas to Solid --- Deposition
are all examples of exothermic processes