An experiment is conducted to determine the charge-to-mass ratio \(q/m\) of an unknown ion. Ions of mass \(m\) and positive charge \(q\) are accelerated from rest through a variable electric potential difference \(\Delta V\) and then enter a region of uniform magnetic field of magnitude \(B\) directed perpendicular to their velocity. The ions follow a semicircular trajectory of radius \(r\), which is measured for several values of \(\Delta V\) while \(B\) remains constant. Which of the following indicates the quantities that should be plotted on the vertical and horizontal axes to produce a linear graph, along with the correct expression for \(q/m\) in terms of the slope \(M\) of the best-fit line and \(B\)?