When the bells are charged up, the left bell acquires a positive charge, the right bell a negative charge. When this occurs, the nut that is suspended between the two bells experiences a torque (it lines itself up with a line between the two bells) but it doesn't experience a net force. What does this tell us about the charge on the nut
Thus simply tells us that The nut has no net charge and so therefore, There will be a negative charge on the left side, and an equal positive charge on the right side