Since the ray strikes the glass slab at an angle of 90°. Therefore

Angle of incidence = 0⁰.

Thus the ray of light will pass straight without any deviation as shown in the figure below.

Laws of Refraction of light;

Refractive index=1.5

Thus angle of refraction is given by

On solving, we get

Thus the angle of refraction is 0^o

Thus the refracted ray is perpendicular to the surface of the glass slab as shown in the above diagram.