The correct answer is a) condensation. Condensation occurs when a gas cools down and transitions into a liquid state. This process is commonly observed when water vapor in the air cools down, forming droplets of water, like when moisture forms on a cold glass.
In contrast, the other options represent different phase changes: b) deposition is the direct change from gas to solid, c) evaporation is the transition from liquid to gas, d) freezing refers to the change from liquid to solid, e) melting is the change from solid to liquid, and f) sublimation is the process where a solid changes directly into a gas. Understanding these terms helps illustrate how matter changes states under various conditions.