Correct Response: C. Fog is composed of small droplets of liquid water suspended in the atmosphere. When fog dissipates, the droplets evaporate and become gaseous water vapor molecules. To move from the liquid phase to the gas phase the water absorbs energy from its surroundings. This makes evaporation an endothermic process. The other three responses all involve exothermic processes in which heat energy is given off by water to its surroundings as it changes phase. When dew forms (A), heat is given off as water vapor condenses into liquid water. During the process of deposition, ice crystals form directly from water vapor (B), releasing heat. Cloud formation (D) occurs as water vapor condenses into liquid water droplets around condensation nuclei, giving off heat energy.
