Clouds form due to which combination?

• A. Water vapor, condensation nuclei, and cooling
• B. Water vapor, heating, and condensation
• C. Water vapor, agitation, and evaporation
• D. Water vapor, solar radiation, and friction

Answer: (A)

Clouds form when water vapor in the air is cooled to its dew point in the presence of condensation nuclei, allowing the vapor to condense into tiny droplets. The cooling lowers the air’s capacity to hold moisture, so when saturation is reached, water vapor starts to condense on the tiny particles—dust, salt, pollen—that act as condensation nuclei. Without those nuclei, condensation is much less efficient, and without cooling to reach saturation, condensation doesn’t readily occur.

So the combination of water vapor, condensation nuclei, and cooling captures the essential steps: moisture source, a surface for droplets to form on, and the process that drives the air to saturation. The other scenarios don’t fit because heating increases the air’s capacity to hold moisture (making condensation less likely), agitation and evaporation promote vaporization rather than forming droplets, and solar radiation and friction don’t directly cause the droplets that make clouds.