When water vapor is cooled, it re-forms into water droplets. Why does this represent a conservation in mass?
50 POINTS!!!

People, especially kids, tend to think that when water evaporates it just disappears, or turns into the air. But we know based on the law of conservation of mass that any time water changes state it keeps the same mass!

Similarly, when water vapor turns to water droplets, when it goes from its gas to its liquid state, it still has the same mass. It's just in a different phase. This is a perfect example of conservation in mass!