Final answer:
When a positively charged rod is near two touching spheres, grounding the second sphere removes its excess charge, leaving it neutral. This manipulation of charge distribution on conductive spheres was demonstrated by Charles Coulomb's experiments.
Step-by-step explanation:
When a positively charged rod is brought near two identical conducting spheres that touch each other, negative charges are attracted to the sphere closer to the rod, leaving the other sphere with an excess of positive charges. Initially, both spheres are neutral, but when they are separated while the rod is still present, each sphere retains a net charge due to the redistribution of charge.
If the sphere further away from the rod is momentarily grounded while the rod is still in place, excess charges will flow to the ground until the potential of the sphere is equal to the ground (which is effectively zero). Because the rod is still in place, the first sphere remains negatively charged while the second sphere becomes neutral. Once the grounding is removed, the second sphere will have no charge as it has lost its excess positive charge to the ground.
Charles Coulomb's experiments with charged spheres demonstrated that when two spheres of the same material, size, and shape came into contact and then separated, the total charge would be equally distributed among them. If these spheres are momentarily grounded, the excess charge is neutralized, leaving the sphere with zero net charge while the other sphere retains its charge.