Final answer:
Both fog and the sky involve the suspension of liquid water droplets in the air, which are visible as clouds and fog due to light scattering. These are natural examples of colloids, which are common in various forms throughout our environment and universe.
Step-by-step explanation:
The substances similar between "fog" and the sky involve liquid water droplets dispersed in air, a phenomenon that occurs naturally in the environment. Fog is created when water vapor condenses into tiny droplets in the air, while in the sky, similar processes create clouds. Both fog and clouds are examples of aerosols, which are suspensions of fine solid particles or liquid droplets in a gas.
In both instances, the appearance of fog or clouds is due to the ability of the tiny water droplets to absorb and scatter light, making them visible. The phenomena involving the dispersion of substances in different states of matter are examples of colloids, which include other forms like smoke, whipped cream, and styrofoam, but it is the interaction between water droplets and air that is common to both fog and the sky. These interactions are governed by the physics of our atmosphere and mirror larger-scale processes in the universe, such as the interaction of gases in the Veil Nebula.