Question

In refraction through a prism if the angle of incidence is equal to angle of emergence like in glass slab then why incident ray is parallel to emergent ray?

Answer 1

If we look at the the refraction through the glass prism diagram, it is evident that the beam of emergent light deviates back in the same direction with respect to the normal. The angle measure with respect to the normal are on the same side (unlike glass slab), so the emergent ray is not parallel to the incident ray.