Consider the ray diagram for the refraction given. The maximum value of angle θ for which the light suffers total internal reflection at the vertical surface, is?

Correct option is B. sin⁻¹(3/4)
At the first refraction
Applying Snell's law
Let angle of refraction be β
1.0sinθ = 1.25sinβ —————(1)
At vertical surface for total internal refraction:
1.25sin(90° - β) = 1
sinβ = 1/1.25
sinβ = 4/5
From eq 1
1.0sinθ = 1.25(4/5)
sinθ = 3/4
Required angle θ = sin⁻¹(3/4)