Well, the force is proportional to the product of the charges
on the two objects. So if the objects are already negatively
charged distance between them is unchanged, then adding
electrons to either or both objects would increase the forces
between them.
Have you ever looked up the density of a substance ? You ought to try it. Go ahead. Pick a substance, then go online or open up an actual book and find its density. You will never see any particular volume mentioned along with the density . . . because it doesn't matter. The whole idea of density is that it describes the substance, no matter how much or how little you have of it. The density of a tiny drop of water under a microscope is the same as the density of a supertanker-ful of water.
A red ladybug appears red in white light, red in red light, and black in blue light. Those would be the proper selections you'd need.
