Final answer:
Rubbing a balloon on wool transfers electrons, giving the balloon a negative charge, while a metal bar allows charges to move freely. Thus, the balloon becomes charged and sticks to the fabric, whereas the metal bar does not become an insulator nor accumulate charges in one location. The correct option is B.
Step-by-step explanation:
When you rub a balloon and a metal bar against a piece of fabric like wool, different effects occur due to the nature of the materials involved. Rubbing a balloon on wool fabric typically transfers electrons from the fabric to the balloon, giving the balloon a negative charge.
This is an example of static electricity. On the other hand, metals are conductors which allow electrons to move freely. This means that when you charge a metal bar by rubbing it against wool, the charges will spread out evenly across the surface of the metal rather than building up in one place as they do with the balloon, which is an insulator.
Therefore, the correct answer to the question is that charges build up in one place on the balloon, the balloon sticks to the wool due to the static electrical charge. Conductors like metal allow charges to move freely to achieve electrostatic equilibrium, and hence a metal bar does not accumulate charges in one location in the same way a balloon does when rubbed with fabric.
The fabric does not act as a conductor in the context of rubbing a balloon or metal bar against it; rather, the wool provides a means for the transfer of electrons due to friction.