Answer
Light does not emerge at Q if the incident angle at P is decreased slightly.
Work Step by Step
If the incident angle at P is decreased slightly, then the angle of refraction $\theta_2$ at P also decreases.
The incident angle at Q is $90^{\circ}-\theta_2$, and this angle increases if $\theta_2$ decreases.
Then the angle of refraction at Q would increase. However, an angle of refraction can not increase to more than $90^{\circ}$
Light does not emerge at Q if the incident angle at P is decreased slightly.
