Answer: a. copper
A magnetic field is a condition of space around a metal or object that causes other objects to be attracted to it. It can be created by passing electricity through an object (usually a magnetic object), as it is the result of electrons in motion.
When electricity is passed through them, iron, nickel, and cobalt are able to produce magnetic fields around themselves, while copper is unable to. When exposed to a magnet, copper is not attracted to the magnet, whereas the electrons on the surface of the copper begin to rotate.