Question

A ray of light passes through four transparent media with refractive indices μ₁, μ₂, μ₃ and μ₄ as shown in the figure. The surfaces of all media are parallel. If the emergent ray CD is parallel to the incident ray AB, we must have
(a) μ₁ = μ₂ (b) μ₂ = μ₃ (c) μ₃ = μ₄ (d) μ₄ = μ₁

Answer 1

we must have 

(d) μ₄ = μ₁