Answer
b. $\vec{F}_{A}$ $_{on}$ $_B = \vec{F}_{B}$ $_{on}$ $_A$
Work Step by Step
Recall that the equation for electric force is $\displaystyle \vec{F}_E = \frac{1}{4\pi\epsilon_0}\frac{q_1q_2}{r^2}$
In this equation, both of the charges are used to calculate the electron force on one another.
Thus, the forces the two charges exert on each other are equal. Option b. is correct.
