Answer:
Negatively charged particles (electrons)
Explanation:
Plastic rod is charged -15.0 nC. It is clear that the charge on the rod is negative so the rod has gain excess of electrons.
When the rod touches a metal sphere charge on the plastic rod remains -10 nC, i.e. negative charge on the rod decreases. This is because negatively charged particles (electrons) are transferred from the plastic rod to the metal sphere.
