A 6.0-mm-diameter copper ball is charged to 70 nC. What fraction of its electrons have been removed? The density of copper is 8900 kg/m³.
a. 2.80 x 10^19 electrons
b. 4.70 x 10^19 electrons
c. 7.60 x 10^19 electrons
d. 1.20 x 10^20 electrons