The subatomic particle possessing the largest
ratio of charge to mass is the:
a neutron
b electron
c proton
d nucleus

B. electrons possess the largest charge-to-mass ratio among the subatomic particles listed in the four choices.

Explanation:

Consider the mass of each particle. Express the masses in atomic mass units:

Similarly, consider the charge on each particle. Express the charges in multiples of the fundamental charge:

Calculate the charge-to-mass ratio for the three species:

Almost all nuclei contain protons and neutrons. The only exception is the hydrogen-1 nucleus, which contains only one proton and no neutron. The mass of the nucleus is approximately the same as the sum of its components' masses. The extra neutron will only add to the mass of the nucleus (the denominator) without contributing to the charge (the numerator.) As a result, the charge-to-mass ratio of nuclei will be positive but no greater than the charge-to-mass ratio of protons.

Among the particles in the four choices, the charge-to-mass ratio is the greatest for electrons.