Answer C, I think. Hope to help :)
The answer should be electron
C. The sum of all forces on an object in equilibrium is zero. Equilibrium means in a stationary position. Therefore there is no acceleration. And using Newton's second law, we can say that the net or resultant force is 0.
F = ma
=>F = m(0)
=>F= 0
I believe it is B. Hope this helps!!
