Mirage is an optical illusion observed in hot deserts. It is entirely caused by: MCQ with Answer and Explanation

In hot deserts, the sand heats the air immediately above it, making it less dense (optically rarer) than cooler air higher up. Light from a tall object (like the sky or a tree) traveling downwards passes from denser to rarer air layers, bending away from the normal. Eventually, the angle of incidence exceeds the critical angle, causing total internal reflection. The observer perceives this reflected light as a pool of water on the ground.