“A ray of light incident on a rectangular glass slab immersed in any medium emerges parallel to itself.” Draw labelled ray diagram to justify the statement.

At the first boundary (air to glass), light travels from a rarer to a denser medium, bending towards the normal. The angle of incidence is $i$ and the angle of refraction is $r_1$. At the second boundary (glass to air), light travels from a denser to a rarer medium, bending away from the normal. The angle of incidence inside the glass is $r_2$ (which is equal to $r_1$ because the normal lines are parallel), and the angle of emergence is $e$. Since the two refracting surfaces are parallel, the angle of incidence $i$ equals the angle of emergence $e$, making the incident and emergent rays parallel to each other.