Four students showed the following traces of the path of a ray of light passing through a rectangular glass slab. The trace most likely to be correct is that of student I, II, III, or IV?

Due to refraction of light inside the glass slab, the incident ray of light turns inwards of the slab and then again refracts at the other surface to obtain a beam of light parallel to the incident light. Clearly IV is rejected since the outgoing beam is not parallel to the incident. Also options I and II are rejected since the bending of light is finite and inwards unlike in the given options respectively. Hence, the correct option is III.