In the figure light is incident at an angle $\mathrm{\theta }$ which is slightly greater than the critical angle. Now, keeping the incident fixed a parallel slab of refractive index n₃ is placed on surface AB. Which of the following statements are correct:

$\mathrm{\theta }$ which is critical angle for refraction from n₂ to n₁ will be more than critical angle between n₃ and n₂ if n₃ < n₁.so, TIR will take place at AB.

Hence,

If n₃ > n₁, then TIR will take place at CD. 

if n₃ < n₁ , then TIR will take place at AB. 

if n₂ > n₃ > n₁ , then TIR will take place at CD.