What must happen for liquid water to become water vapor?

a. the water molecules must lose energy and stop moving.

b. the water molecules must exert less pressure on their container.

c. the water molecules must gain kinetic energy.

d. the water molecules must lose heat and gain volume.

C. The water molecules must gain kinetic energy.

Option (C) is the correct answer.

Explanation:

When liquid water is heated then molecules of water absorb heat and due to this vibration between water molecules increase to greater extent. As a result, kinetic energy of water molecules also increases.

Therefore, water starts to evaporate as the temperature reaches at 100 degree Celsius.

Thus, we can conclude that the water molecules must gain kinetic energy for liquid water to become water vapor.