Answer
See explanation.
Work Step by Step
To give the metal sphere a net negative charge, touch the negatively-charged object to it while it is on the insulated stand.
To give the metal sphere a net positive charge, follow the procedure in Figure 21.7. First ground the metal sphere. Bring the negatively charged object near the sphere. Electrons will be repelled out of the sphere through the ground wire. Now, keeping the charged object nearby, isolate the sphere. It will be left with a net positive charge.
