Total Internal Reflection question from NEET 2001 (AIPMT)

Answer: (b)

1. Light escapes only inside a circle where it meets the surface at less than $C$: $R = h\tan C = \frac{h}{\sqrt{n^2-1}}$.
2. $\sqrt{n^2-1} = \sqrt{\frac{25}{9}-1} = \frac{4}{3}$.
3. $R = \frac{4}{4/3} = 3$ m.
4. So the answer is (b) 3 m.