Arrange the following in the correct order as the angle of incidence…

The correct answer is Option (3) → (D), (A), (B), (C)

When light passes from a denser to a rarer medium, Snell’s law \( n_d\sin i = n_r\sin r \) gives \( r \gt i \), and the angle of refraction reaches 90° at the critical angle \( i_c \), where \( \sin i_c = n_r/n_d \). Follow what happens as i increases from zero:

(D) The ray passes undeviated when incident normally. At i = 0, r = 0, so the ray goes straight through.

(A) The refracted ray bends away from the normal. For \( 0 \lt i \lt i_c \), \( \sin r = (n_d/n_r)\sin i \) is larger than \( \sin i \).

(B) The refracted ray grazes along the surface of separation. At \( i = i_c \) the angle of refraction becomes 90°.

(C) The light is totally reflected back into the denser medium. For \( i \gt i_c \) no refracted ray is possible, so total internal reflection occurs.

So the order is (D), (A), (B), (C).

NCERT (2026-27):
Total Internal Reflection – “… When a ray of light enters from a denser medium to a rarer medium, it bends away from the normal, for example, the ray AO₁B in Fig. 9.11.”

Total Internal Reflection – “… As the angle of incidence increases, so does the angle of refraction, till for the ray AO₃, the angle of refraction is \( \pi/2 \). The refracted ray is bent so much away from the normal that it grazes the surface at the interface between the two media. … If the angle of incidence is increased still further (e.g., the ray AO₄), refraction is not possible, and the incident ray is totally reflected. This is called total internal reflection.”