If an incident ray falls normally on a glass slab, then what will be the angle of incidence and angle of refraction?

If the rays are perpendicular to the glass slab then i = 0⁰, sin i = 0.

Then, sin r = sin i/µ = 0/µ = 0

Therefore, r = 0⁰

That is no bending of the refracted ray.
Regards