PQR is a right angled prism with other angles as 60° and 30°. Refractive index of prism is 1.5. PQ has a thin layer of liquid. Light falls normally on the face PR. For total internal reflection, maximum refractive index of liquid is

1.2

For TIR at PQ:  θ > C

From the geometry of figure: θ = 60°

So, 60° > C  ⇒  sin 60° > sin C

$\Rightarrow \frac{\sqrt{3}}{2}>\frac{\mu_{\text {Liquid }}}{\mu_{\text {Prism }}} \Rightarrow \mu_{\text {Liquid }}<\frac{\sqrt{3}}{2} \times \mu_{\text {Prism }} \Rightarrow \mu_{\text {Liquid }}<\frac{\sqrt{3}}{2} \times 1.5 \Rightarrow \mu_{\text {Liquid }}<1.3$