Which element is magnetic?

• A. calcium
• B. chromium
• C. carbon
• D. cobalt

Answer: (D)

Cobalt is classified as a magnetic element due to its specific atomic structure and electron configuration. It is a transition metal located in Group 9 of the periodic table and possesses unpaired electrons in its d-orbitals, which allows it to exhibit ferromagnetism at room temperature. This property means that cobalt can not only be magnetized but also maintain its magnetic properties even after the external magnetic field is removed.

In contrast, while chromium has some magnetic properties, it is not typically classified as a magnetic element like cobalt due to its weaker ferromagnetic characteristics at standard conditions. Calcium and carbon do not exhibit magnetic properties in the same way, as calcium is an alkaline earth metal and carbon is a non-metal; both lack unpaired electrons necessary for ferromagnetism. Therefore, cobalt stands out as the clear answer.