Emergent ray is parallel to the incident ray, after the refraction of Incident ray through a glass slab because the angle of incidence is equal to the angle of emergence and they are also the alternate interior angles.

Why is refracted light parallel?

A ray of light passes through the air (yellow) to a glass plate (blue) and then back into the air. By Snell's law, the angles of refraction at the first and second surfaces are equal and therefore the entry and exit rays are parallel.

Why is a refracted ray parallel to the base of a prism?

For an equilateral prism, when it is kept in minimum deviation position, the refracted Ray is parallel to the base of the prism. Answer: at minimum deviation position the refracted ray is parllel to base.