The correct answer is C. Total internal reflection.
Refraction is the bending of light as it passes from one medium to another. The amount of refraction depends on the angle of incidence, the refractive indices of the two media, and the wavelength of light.
When light passes from a medium with a higher refractive index to a medium with a lower refractive index, the angle of refraction is greater than the angle of incidence. This is because the light waves slow down as they enter the lower-index medium.
The critical angle is the angle of incidence at which the angle of refraction is 90 degrees. If the angle of incidence is greater than the critical angle, then no light will be refracted into the second medium. All of the light will be reflected back into the first medium. This is called total internal reflection.
Total internal reflection can occur when light passes from a medium with a high refractive index to a medium with a low refractive index. For example, it can occur when light passes from water to air.
Total internal reflection is used in many optical devices, such as fiber optic cables and periscopes.