What happens when heat is added to a refrigerant?

When heat is added to a refrigerant, it primarily causes the refrigerant to vaporize. This process occurs because adding heat increases the energy of the refrigerant molecules, allowing them to overcome intermolecular forces. As the temperature rises, the refrigerant absorbs the heat, which facilitates the transition from a liquid state to a gaseous state, thus matching the behavior that is characteristic of most refrigerants during heating.

The vaporization process is fundamental in refrigeration cycles as it allows the refrigerant to absorb heat from the environment or a space being cooled. When refrigerant vaporizes, it can thus carry away heat, maintaining the cooling effect.

The other options do not correctly represent the behavior of refrigerants under the influence of added heat. Liquefying occurs under specific pressure conditions and typically when heat is removed, while solidification implies a phase change to solid, which happens when heat is removed. The notion of a change to gas without increasing temperature is related to phase changes at specific pressures and is not typical for refrigerants under standard operational conditions. Hence, the most accurate response is that adding heat to a refrigerant leads to its vaporization.