Select the sentence that best describes why copper and some other metals are good conductors.

a) copper atoms have loosely held electrons; this means they can freely move in and out of the nucleus of the atom.
b) copper atoms have a loosely held free electron in their outer shell that is able to move freely to other atoms.
c) copper and some other metals have highly active inner shells. this means that electrons can be freely exchanged between shells.
d)copper has a small number of electrons; this means it can easily shed these electrons and take electrons from other atoms.