This is a multiple choice question. Please show step-by-step. Thank you!

5. Light is incident along the normal to the short face of a 30-60-90 glass prism (n = 1.50). A drop of liquid is placed on the top surface of the prism. If this 30 60 ray strikes the interface between the glass-film boundary at the critical angle, then what is the index of refraction for the oil? 90 (1) 1.3 (2) 3.0 (3) 0.75 (4) 1.7 (5) 1.0