Correct Option
Paramagnetism is a form of magnetism where materials are weakly attracted by an external magnetic field. This property arises from the presence of unpaired electrons in their atoms or molecules. Molecular oxygen (O₂) exhibits paramagnetism because its molecular orbital configuration reveals the presence of two unpaired electrons, which accounts for its weak attraction to a magnetic field. This characteristic has been experimentally verified.
Incorrect Options
Iron (Fe) is a ferromagnetic material. Ferromagnetic substances are strongly attracted to magnetic fields and can retain their magnetism even after the external field is removed, due to the presence of domains with aligned magnetic moments.
Molecular hydrogen (H₂) is diamagnetic. Diamagnetic materials are weakly repelled by magnetic fields, a property attributed to the absence of unpaired electrons, meaning all electrons are paired in their orbitals.
Molecular nitrogen (N₂) is also diamagnetic. Similar to hydrogen, all electrons in the N₂ molecule are paired, resulting in no net magnetic moment and a weak repulsion from external magnetic fields.