Which of the following molecules is diamagnetic according to molecular orbital theory? A) N₂⁺ B) N₂⁻ C) CN D) CN⁻

D) CN⁻

Explanation:

    Hund's Rule of Maximum Multiplicity state that electrons go into degenerate orbitals of sub-levels (p,d, and f ) singly before pairing commences. Hund's rule is useful in determining the number of unpaired electrons in an atom. As such, it explains some magnetic properties of elements.

An element whose atoms or molecules contain unpaired electrons is paramagnetic. i.e., weakly attracted to substances in a magnetic field.

On the other hand, the element whose atoms or molecules are filled up with paired electrons is known as diamagnetic, i.e., not attracted by magnetic substances.

According to the molecular orbital theory, the diamagnetic molecule is CN⁻ because of the absence of unpaired electrons.