Question

what is total internal reflection ?how can you observe it​

Answer 1

total internal reflection is the  complete reflection of a ray of light within a medium such as water or glass from the surrounding surfaces back into the medium

Answer 2

when a Ray of light travelling in a denser medium is incident at the surface of a rera medium at the angle of incidence greater than the critical angle for the pair of media the ray is totally reflected back into the denser medium this phenomenon is called total internal reflection.

Essential conditions for total internal reflection

The light must travel from a denser to rarer medium

the angle of incidence must be greater than the critical angle for the pair of media