Which is not an application of Total Internal Reflection:

The correct answer is Option (3) → Advance sunrise and delayed sunset

Total internal reflection occurs when light travelling from a denser to a rarer medium meets the boundary at an angle greater than the critical angle. Each option is checked against this condition.

Option (1) Mirage — Application of TIR. Light from a tall object passes through layers of air that get rarer towards the hot ground, bends away from the normal and is totally reflected.

Option (2) Brilliance of diamond — Application of TIR. The critical angle of diamond is small (about \( 24.4^\circ \)), so light entering it is totally reflected many times before leaving, which makes it sparkle.

Option (3) Advance sunrise and delayed sunset — Not an application of TIR. It is due to atmospheric refraction: the refractive index of air increases towards the ground, so sunlight bends gradually and the Sun is seen a little before it actually rises and a little after it actually sets. No reflection is involved.

Option (4) Optical fibre — Application of TIR. Light is guided along the fibre by repeated total internal reflections at the core-cladding boundary.

NCERT (2026-27):
Summary – “… The critical angle of incidence \( i_c \) for a ray incident from a denser to rarer medium, is that angle for which the angle of refraction is \( 90^\circ \). For \( i \gt i_c \), total internal reflection occurs. Multiple internal reflections in diamond (\( i_c \cong 24.4^\circ \)), totally reflecting prisms and mirage, are some examples of total internal reflection. Optical fibres consist of glass fibres coated with a thin layer of material of lower refractive index. Light incident at an angle at one end comes out at the other, after multiple internal reflections, even if the fibre is bent.”