What Is the Critical Angle for Diamond (N = 2 $^{\circ}$

Multiple Choice

What is the critical angle for diamond (n = 2.42) ?

A) 2.42 $^{\circ}$
B) 67.5 $^{\circ}$
C) 65.6 $^{\circ}$
D) 24.4 $^{\circ}$
E) 37.1 $^{\circ}$