Which of the following effect can be observed when a fine beam of light enters a room through a small hole?

Tyndall effect

The correct answer is option 3. Tyndall effect.

Tyndall effect can be observed when a fine beam of light enters a room through a small hole.

This happens due to the scattering of light by the particles of dust and smoke in the air making its path visible.

Tyndall effect can be observed when sunlight passes through the canopy of a dense forest. In the forest, mist contains tiny droplets of water, which act as particles of colloid dispersed in air.