When a ray of light travels from an optcally denser to an optically rarer medium, it reflects back to the denser medium at the interface without entering the rarer medium. This phenomenon is called:

The correct option is B Total internal reflection
When a ray of light passes from a medium of higher optical density to a medium of lower optical density at an angle of incidence greater than the critical angle, the ray is reflected back to the same medium. This phenomenon is called total internal reflection.