A light ray is incident on a rectangular glass slab at an angle of ${60}^{\circ }$. The angle between the ray coming out of the slab and the normal to the face of the rectangular slab from which it comes out is ____________?

The angle of incidence is the angle between the incident ray and the normal.
The angle of incidence $= {90}^{\circ }-{{60}^{\circ }}^{ }$$= {30}^{\circ }$
In the rectangular slab, the angle of emergence is equal to the angle of incidence. 

Hence, the angle of emergence is ${30}^{\circ }$.