Total internal reflection occurs when to angle of refraction is 90 degrees; in other words, there is no refraction: the light is reflected completely. The angle of incidence at which this occurs is the critical angle. Any angle beyond that will result in total internal reflection.
The last ray of light (60 degrees) results in total internal reflection. This means that the critical angle is 60 degrees, and that any angle greater than that will result in total internal reflection.
