The direction of ray of light incident on a concave mirror is shown by PQ while directions in which the ray would travel after reflection is shown by four rays marked 1,2,3 and 4 (Figure). Which of the four rays correctly shows the direction of reflected ray?

Incidence ray PQ is coming through principal focus F so it must be parallel to principal axis, that is, either 2 or 4 .
As it is a concave mirror so, ray cannot go behind the mirror so ray (4) is discarded.
So, ray 2 is the reflected ray that verifies answer (B),