Two identical conducting spheres are initially separated. The left sphere has a -3 coulomb charge and the right sphere has a +2 coulomb charge. The spheres are allowed to touch each other briefly, and then they are separated. Determine the charge on the left sphere.
The answer is (B), what I don't understand is that when the spheres touch, their excess charges neutralize, and each sphere ends up having the same charge. Why is this? Is this because they are both conductors and when conductors touch, both conductors end up having the same charge each? Is this because one charge is positive and the other is negative?