What is Hund's rule? What is Hund's rule? When filling orbitals of equal energy, electrons fill them singly first, with parallel spins. The maximum number of electrons in an orbital is eight. The chemical properties of elements are largely determined by the number of valence electrons they contain. The maximum number of electrons in an orbital is two.

Option A

Explanation:

Hund's rule expresses each orbital in a sub-shell is independently occupied with one electron before any one orbital is doubly involved, and all electrons in separately involved orbitals have a similar turn.

It expresses that when filling degenerate orbitals, electrons fill them separately first, with parallel spin. This is the aftereffect of a molecule's propensity to locate the most reduced energy state conceivable.