Answer
We can rank the kinetic energies of the particles at point $B$:
$alpha~particle \gt electron = proton$
Work Step by Step
We can use Equation (24-9) to write an expression for the change in kinetic energy:
$\Delta K = -q~\Delta V = -q~(V_B-V_A)$
We can find the kinetic energy of each particle:
electron:
$K = -(-1e)(100~V) = 100~eV$
proton:
$K = -(1e)(-100~V) = 100~eV$
alpha particle:
$K = -(2e)(-100~V) = 200~eV$
We can rank the kinetic energies of the particles at point $B$:
$alpha~particle \gt electron = proton$
