Answer : (C) refraction.
Explanation :
This figure shows the refraction of light. Refraction of light is the phenomena in which light rays bend at the boundary of two medium.
When a light ray moves from denser to rarer medium then it will bend away from the normal line.
And if it moves from rarer to denser medium then it will bend toward the normal line.
Refraction of light depends on the refractive index of the medium.
So, the correct option is (C) "refraction"
