The correct answer is (b) Refraction
When a beam of light is passed from one medium to another medium then the beam of light bends when it passes from one medium to other, this phenomenon is called as Refraction. This change can be determined by measuring the change in the wave speed and the initial direction of wave relative to the direction of the change in speed. Example: when a beam of light is passed through a prism, when a laser light is passed through a ice cube.