Conservation of Charge Problem [closed]

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.

(A)-1C

(B)-1/2 C

(C)0 C

(D)1/2 C

(E)1 C

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?

closed as off-topic by AccidentalFourierTransform, Cosmas Zachos, Qmechanic♦Jun 22 '18 at 3:05

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – AccidentalFourierTransform, Cosmas Zachos, Qmechanic
If this question can be reworded to fit the rules in the help center, please edit the question.

1) Charges of opposite sign cancel.

2) Charges distribute themselves for maximum seperation on a conductor's surface.