91Ó°ÊÓ

The given figure of light transmission gives the change of light path through three different layers b, c, and d due to refraction.

For a material with a higher refractive index, the light bends towards the normal line; while for a material with a low refractive index, it speeds up and bends away from the normal line.

When light travels from a rarer to a denser medium, it refracts towards the normal, and when it travels from a denser to a rarer medium, it refracts away from the normal.

Analyzing the given figure according to this, we can write that

$$\begin{gathered} n_b>n_a \\ {n}_b>n_c \\ {n}_d>n_c \\ {n}_d>n_a \end{gathered}$$

From this, we can conclude that

$n_d>n_b>n_c>n_a\mathrm{or}{n}_d>n_b>n_a>n_c$

The angle made by the light ray with the surface in material a is greater than that with material c.

Hence, by Snell’s law, $n_c>n_a$

Therefore, the ranking of the materials is$n_d>n_b>n_c>n_a$