Let \(C\) by critical angle \(\mu=2=\frac{\sin i}{\sin r}\)
\(i_e=90^{\circ}\)
\(60^{\circ}=r+C \text { from geometry }\)
\(\frac{1}{\mu}=\frac{1}{2}=\frac{\sin C}{\sin i_e}\)
[At emergent interface]
\(C=\sin ^{-1} \frac{1}{2}=30^{\circ}\)
\(r=30^{\circ}\)
\(\frac{\sin i}{\sin r}=2\)
\(\sin i=1\)
\(i=\frac{\pi}{2}\)