Which rare element is highly metallic and magnetic?

• A. Iron
• B. Copper
• C. Gadolinium
• D. Aluminum

Answer: (C)

Rare-earth metals have electrons in the f orbitals that create large magnetic moments. Gadolinium, a rare-earth metal, stands out because it has a high density of unpaired electrons, giving it a strong magnetic behavior compared with other common metals. This combination of being a rare element and exhibiting pronounced magnetic properties makes gadolinium the best answer. The other options are metals, but none are both rare and notably magnetic (iron is magnetic but not rare; copper and aluminum are not magnetic in any strong sense).