According to question a ray of light falls perpendicularly which means angle of incidence = 0. if angle of incidence is 0 then light ray doesn’t refract and moves in a straight line.
if Refractive index of the prism = 1.5 then critical angle is given by
critical angle = arcsin(1/refractive index)
critical angle = arcsin(1/1.5) = 41.81
the figure looks something just like this.
from figure we know when it hits the larger face , the angle of incidence is 45. since angle of incidence is greater than that of critical angle there is total internal reflection.
total deviation would = 2* glancing angle in our case glancing angle is 45. so deviation would be 90.