The path of a ray of light passing through a rectangular glass slab tested by four students are shown in Figure as A, B, C and D. Which one of them is correct?

The light ray, on entering the rectangular slab, is bent towards the normal since the medium of rectangular slab is denser than the air medium present outside. On leaving the slab, it is refracted away from the normal.

NOTE: The phenomenon shown above is called refraction. When light passes from a rarer to denser medium, it is refracted towards the normal. When light passes from denser to rarer medium, it is refracted away from the normal.