Correct Answer: total internal reflection by layers of air

Solution : The correct answer is total internal reflection by the layers of air.

Mirage is the appearance of an illusion of water body in desert areas or a water pool on road on hot summer days. It happens because of the total internal reflection of the light by the layers of air. Due to to differential heating of air above the ground the incident light rays are sometimes totally internally reflected when they travel from cool denser air medium to a hot rarer air medium. This total internal reflection creates a U shaped bend because of which mind interpreted the ground as a light source rather than the object above. Because of this Mirage is formed.