Which of the following species is ferromagnetic?

Correct option is C

Ferromagnetism is a property of certain materials (such as iron) that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet. Ferromagnetic materials are noticeably attracted to a magnet, which is a consequence of their substantial magnetic permeability.

CrO₂ (Chromium dioxide) is a ferromagnetic material due to its unique electron configuration and magnetic ordering. It has unpaired electrons that align parallel to each other in the presence of a magnetic field, leading to a strong, permanent magnetism.
Oxygen in its diatomic form is paramagnetic due to the presence of unpaired electrons.
Benzene is diamagnetic as it has no unpaired electrons in its π-electron cloud.
Information Booster
Diamagnetism is the tendency of a substance to oppose an applied magnetic field and hence to be repelled by a magnetic field.
The electron spin of unpaired electrons causes paramagnetism. When a group of electrons is subjected to a magnetic field, the dipole moments of the electrons seem to line up with the field, just like a tiny bar magnet.
Ferromagnetism only occurs in some substances like iron, nickel, cobalt, their alloys, and some alloys of rare-earth metals.