The optical density of turpentine is higher than that of water while its mass density is lower. Fig 9.2. shows a layer of turpentine floating over water in a container. For which one of the four ray’s incident on turpentine in Fig 9.2, the path shown is correct?

As air is optically less dens than turpentine, a ray coming from air should bend towards the normal at the turpentine-air interface. We have drawn normal lines as dotted orange lines for clarity.

We can eliminate ray 4 and ray 3 as ray 3 goes undeflected and ray 4 bends away from the normal. Hence, option (c) and (d) are incorrect.

Let us consider the turpentine-water interface. As turpentine is optically denser than water, rays coming from the former to the latter, should deflect away from the normal. We have drawn the normal lines as dotted purple lines at the turpentine-water interface for ray 1 and ray 2.

Only ray 2 out of the two rays bends away from the normal. Hence, the correct option is (b).