Clouds, fog, or dew will always form when which process occurs?

• A. Water vapor condenses
• B. Water vapor evaporates
• C. Air cools rapidly
• D. Humidity rises

Answer: (A)

Condensation is the key process. When water vapor in the air loses enough energy, it changes into liquid water. Those tiny droplets form around condensation nuclei and gather to create visible phenomena: clouds high in the sky, fog near the ground, or dew on surfaces such as a wing. Evaporation would reverse this, turning liquid water back into vapor, so it wouldn’t produce droplets. Merely increasing humidity adds more water vapor, but without cooling to the dew point (or mixing with cooler air) the air may remain unsaturated and no condensation occurs. Rapid cooling helps push the air to saturation, but condensation is the actual step that creates the droplets needed for clouds, fog, or dew.