Cindy saw her mother heating a wet pan on the stove. as the pan got hotter, the water on the outside began to dry. why?

As the temperature of materials increase, the objects find a phenomenon called change of phase.

This means that if you give enough heat to a liquid, this can change of state from liquid state to gas state (the water evaporates)

So the water in the pan reaches the evaporation temperature (around 100°C) and it starts to evaporate, this is why the water on the outside begins to "dry"

the answer would be a