Final answer:
When a negatively charged rod touches a neutral metal sphere, excess electrons from the rod are transferred to the sphere, causing it to become negatively charged as well. This is due to the mobility of electrons in metals and the sphere will retain this charge once the rod is removed.
Step-by-step explanation:
When a negatively charged rod touches a neutral metal sphere on an isolated stand, the excess electrons on the rod will be transferred to the sphere, causing the sphere to become negatively charged as well. This occurs because metals have free electrons that can move easily throughout the metal. Since the negatively charged rod has an excess of electrons, some of them will move to the sphere to distribute the charge more evenly. Once the rod is removed, the sphere retains the excess negative charge. This is an application of the basic principles of static electricity and charge transfer.
In a similar scenario with a positively charged rod, electrons on the neutral metal sphere would be attracted to the point of contact and some would transfer to the rod, leaving the sphere with a net positive charge. Both outcomes demonstrate conduction, which is one way to charge an object.