Concept:Evaporation occurs when the fastest-moving molecules at the liquid surface gain enough energy to break free into the air.
Explanation:Liquid molecules are in constant motion with different kinetic energies.
Only molecules near the surface can escape directly into the air.
The most energetic molecules can overcome the attractive forces of the other liquid molecules.
They leave the liquid surface and escape as vapour, causing the liquid level to fall gradually.
Less energetic molecules generally do not have enough energy to escape.
This continuous escape of high-energy molecules is the process of evaporation, which explains why the amount of liquid decreases over time.
Answer:Option A: The most energetic molecules leave the surface and escape into the air.