Final answer:
Cobalt is the hard magnetic metal used in steel production, and its isotope, Cobalt-60, is used in cancer treatment due to its emission of gamma rays.
Step-by-step explanation:
The answer to the question regarding a hard magnetic metal used in the production of steel and a radioactive form of this element used in cancer treatment is a. Cobalt. Cobalt is a transition metal and ferromagnetic, which makes it useful in the production of steel and other alloys. The radioactive isotope Cobalt-60 is produced by the neutron activation of Co-59, which then undergoes decay to form Ni-60, along with the emission of gamma radiation. This isotope is used in medicine for the treatment of cancer due to its ability to emit high-energy gamma rays, which can destroy cancer cells.