Why do water droplets form outside a cold bottle?

Correct answer: Water vapour in air condenses

Correct answer: B, water vapour in the air condenses. The air around the bottle contains invisible water vapour. When this moist air touches the cold outer surface, the nearby air is cooled. If it reaches its dew point, it cannot retain all the vapour in the gaseous state, so some vapour changes into liquid droplets on the bottle. The water therefore comes from the surrounding air, not through the bottle wall. A is wrong because an intact bottle does not release its contents through its surface. B is correct because it describes the condensation process. C is wrong because the bottle is not melting; melting is the change of a solid into a liquid. D is wrong because dust does not turn into water, although tiny particles can sometimes provide surfaces for droplets to form. This everyday example shows that condensation can occur on a cold surface. Memory cue: cold surface plus moist air produces outside droplets.