Formation of water droplets on a cold bottle occurs due to which process?

Correct answer: Condensation

Direct answer: Option C, condensation. Condensation is the change of a gas or vapour into a liquid. Air always contains some water vapour. When a bottle is colder than the surrounding air, the water vapour touching its cold outer surface loses heat. It changes into tiny liquid-water droplets, which we see on the bottle. Step by step: water is present in air as invisible vapour; the cold bottle cools the nearby vapour; the vapour changes state from gas to liquid; liquid droplets collect on the surface. Option A, melting, means a solid changes into a liquid, such as ice becoming water, so it does not describe water vapour in air. Option B, sublimation, means a solid changes directly into a gas, such as solid carbon dioxide changing to gas; no such change is involved here. Option C is correct because gas becomes liquid. Option D, freezing, means a liquid changes into a solid, such as water becoming ice; the droplets on the bottle are liquid, not solid. Important exam cue: the water comes from the air, not usually through the bottle. Remember: cooling vapour gives condensation.