What occurs when light moves from one transparent medium to another?

When light transitions from one transparent medium to another, its speed changes due to variations in the optical densities of the two media. This change in speed is what leads to refraction, which is the bending of light as it passes through the boundary between the two media. For example, when light moves from air into water, it slows down and bends towards the normal line (an imaginary line perpendicular to the surface) because water is denser than air. This principle is fundamental in understanding phenomena such as lenses and prisms, which use the bending of light to focus or disperse light beams.

The other options do not accurately describe what happens during this transition. For instance, the speed of light does not remain constant across different media, and it is not absorbed completely in a typical medium transition. Scattering, on the other hand, refers to a different interaction of light, where it is deflected in many directions, usually occurring in opaque materials rather than transparent ones. Thus, option C accurately captures the behavior of light during the transition.