How can abundance of condensation nuclei affect urban fog?

Correct answer: It provides more surfaces for tiny droplets to form

Correct answer: A. Condensation nuclei are tiny particles, such as suitable dust, smoke, or pollution particles, on whose surfaces water vapour can condense. Urban air often contains many such particles. When moist air cools to saturation, the abundance of nuclei provides numerous sites for small water droplets to begin forming, which can support the development or thickening of fog when other conditions are favourable. A is correct because it describes the physical role of these particles. B is wrong because nuclei do not remove all water vapour; they help convert some vapour into droplets. C is wrong because adding particles does not make air completely dry. D is wrong because fog changes to frost only under appropriate freezing conditions, not simply because nuclei are abundant. Memory cue: nuclei are “seeds” for droplets, not water removers. Pollution may increase available nuclei, but moisture and cooling are still necessary for fog.