Answer:
- See the diagram attached: the ray of light passes straight through a parallel-sides glass block when it hits the glass at 90º.
Step-by-step explanation:
When the ray of light hits the the glass at 90° (that is, perpendicular to the glass), the ray is parallel to the normal and it will not change its direction when it enters: it will go straight through the glass block. It will not refract.
Also, since the other side, through which the ray of ligth will emerge, is parallel to the first side, the ray will be perpendicular to the emerging surface and, again, will not refract.
In conclusion, the ray of light passes straight through a parallel-sides glass block when it hits the glass at 90º.