Question

a ray of light in incident normally on a plane glass slab what will be the angle of refraction , and the angle of deviation for the ray​

Answer 1

The ray of light which is incident normally on a plane glass slab passes undeviated. That is such a ray suffers no bending at the surface because here the angle of incidence is 0°. Thus if angle of incidence ∠i= 0°, then the angle of refraction ∠r = 0°. And the angle of deviation of the ray will also be 0°.