What are fog and clouds primarily composed of?

Fog and clouds are primarily composed of tiny water droplets. These droplets form when water vapor in the atmosphere cools and condenses into liquid form. The presence of these tiny droplets creates the visible phenomena that we observe as fog or clouds.

As the air cools and reaches a point known as the dew point, the water vapor condenses on small aerosol particles, leading to the formation of these droplets. In the case of fog, the condensation occurs close to the Earth's surface, resulting in reduced visibility. For clouds, the process occurs at varying altitudes, and the size and density of the droplets can vary, leading to different types of cloud formations.

While water vapor is indeed the gaseous form of water essential for saturation and condensation, it is the tiny water droplets that constitute the physical makeup of fog and clouds. Ice particles can also exist in clouds, particularly at higher altitudes where temperatures are colder, but they are not the primary component of typical clouds and fog. Lastly, oxygen molecules are a basic component of the atmosphere but do not contribute to the formation of fog or clouds in terms of their composition.