When the air starts to cool and water vapour condenses, fog is formed. It is a visible aerosol made up of very small water droplets that is always near to the surface of Earth.
Scattering is when light deviates from its straight route due to the particles suspended in the medium.
Step 2: Fog is not visible
The water droplets present in the fog scatter the light in every direction.
Instead of seeing anything beyond a few metres, the spectator sees just a whiteout.
Hence, one cannot see through fog because of the water droplets present in the fog, which scatter lights in all direction.