Minimum refractive index for total internal reflection in a prism

[crystalplane]

Homework Statement

a)What is the minimum refractive index of the prism in order for the light to reflect?
b) What is wrong with this ray path for a reflecting prism?

Homework Equations

n_isin(theta 1)= n_tsin(theta 2)

The Attempt at a Solution

for part a, n_t is 1, theta 2 is 90 degree, theta 1 is 50 degree,
then i got n_i = 1.3
For part b, i have no idea about it..

 

[crystalplane]

the graph is attached now...