A periscope is an optical instrument that allows the viewer to see objects that are not in the direct line of sight. It consists of two mirrors or prisms that are positioned at an angle to each other. The functioning of a periscope is based on the principle of reflection of light.

Option 1: Reflection of light - This is the correct answer. When light falls on a mirror or prism, it reflects off the surface, allowing us to see the image. In a periscope, the first mirror captures the light from the object and reflects it upwards to the second mirror, which then reflects it towards the viewer`s eye. This way, the viewer can see objects that are above the line of sight.

Option 2: Refraction of light - Refraction occurs when light passes through a medium and changes direction. While refraction is a natural phenomenon, it is not the principle behind the functioning of a periscope.

Option 3: Dispersion of light - Dispersion refers to the splitting of light into its component colors. It is not relevant to the functioning of a periscope.

Option 4: Total internal reflection of light - While total internal reflection can occur in certain situations, it is not the natural phenomenon that a periscope