A narrow beam strikes a smooth vertical wall at point P. The incident beam travels in the horizontal plane making 25∘ with the wall surface (measured within that plane). Before drawing the reflected beam, the student must draw the normal at P so that the first law of reflection is satisfied. Which of the following correctly describes the required position of the normal?
a) A vertical line perpendicular to the floor
b) Any line perpendicular to the wall surface irrespective of its plane
c) A line perpendicular to the wall surface lying in the same horizontal plane as the incident beam
d) A line that bisects the angle between the incident beam and the wall surface in the horizontal plane