What can always be said about a negatively-charged ion? A negatively-charged ion always has more neutrons than protons
A negatively-charged ion always has more electrons than protons
A negatively-charged ion always has more protons than electrons
A negatively-charged ion always has more protons than neutrons

A negatively-charged ion always has more electrons than protons

Explanation:

First, we know that the elementary negative charge is the electron, while the positive one is the proton. Such that both have the same charge in magnitude, but a different sign. Such that if we have the same number of electrons and protons in an atom, the charge of this atom will be neutral.

And an ion is an atom with a different number of electrons and protons, so the charge of the atom is not neutral.

Then if we have a negatively-charged ion, the charge of this atom is negative. Then we must have a larger number of electrons (the negative ones) than protons (the positive ones)

Then the correct option is:

A negatively-charged ion always has more electrons than protons

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.