Question

During refraction of light through the glass slab incident ray and emergent ray are parallel to each other explain

Answer 1

Since the refracting surface are parallel to each other the emergent rays are parallel.... Since the surface are parallel the ray inside the glass falls at the other surface at angle r and therefore the ray emerges at angle i that is the angle of incidence. Therefore the incident ray is parallel to the emergent ray.
Hope helped

Answer 2

since the refractive angles at both the time i.e when it goes from medium 1 to medium 2 and then from medium 2 to medium 1

corresponding angle test can be applied over here