While performing the experiment on tracing the path of a ray of light through a rectangular glass slab, in which of the following experimental setups, students likely to get the best results?

The pins must not be too close to each other, otherwise, it would be hard to align the light passing through both of them when seen from the other side of the slab. Hence I and IV are rejected. Also, the angle of incidence and the distance of the point of incidence from the mid slab must be optimum for observing the shifted path of light after emergence from the other side of the slab. So, II is rejected. Hence, the correct answer is option III.