Why is water vapour alone not enough for condensation to begin?

Correct answer: Because cooling and condensation nuclei are also needed

The correct answer is A. Condensation is the change of water vapour into liquid water, and it normally begins when moist air cools to its dew point. Cooling reduces the energy of water molecules and makes liquid formation possible. In the atmosphere, tiny particles such as dust, smoke, or salt can act as condensation nuclei. Water molecules gather on these particles and form droplets more readily. Water vapour may sometimes remain in a supersaturated state if suitable nuclei are absent, so vapour alone is not the complete explanation. B is wrong because fire heats air and is not required for condensation. C is wrong because water vapour is the gaseous state of water, not a solid. D is wrong because condensation occurs at the surface, in clouds, and in many other places, not only underground. Memory cue: condensation needs cooling to the dew point and a place or particle on which droplets can form.