The correct answer is option 2: Rays of light are scattered by the fog droplets.

Fog consists of tiny water droplets suspended in the air. These droplets are similar in size to the wavelength of visible light. When light encounters these droplets, it interacts with them in a process called scattering.

Scattering occurs because the fog droplets cause the light to change direction as it passes through them. This causes the light to be spread out or scattered in different directions. As a result, the light that reaches our eyes is no longer in a straight path, making it difficult to see through the fog clearly.

In contrast to fog, air with clear visibility contains fewer particles, and the particles present are generally much smaller than the wavelength of visible light. This allows light to travel through the air without significant scattering, resulting in clear visibility.

It`s important to note that the other options are not the primary reasons for the difficulty in seeing through fog. Option 1 about total internal reflection and option 4 about the refractive index of fog are not accurate explanations for fog`s visibility issues. Option 3 about fog droplets absorbing light is also not the main reason for the reduced visibility, as scattering is the primary factor at play.