Question

what is hunds rule?
when filling orbitals of equal energy, electrons fill them singly first, with parallel spins.
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.
the maximum number of electrons in an orbital is eight.

Explanation:

Hund's rule specifically pertains to electron - filling in degenerate (equal - energy) orbitals. It states that electrons will occupy these orbitals singly first with parallel spins before pairing up.
The second option is related to the valence - electron concept (not Hund's rule). The third option is the Pauli exclusion principle. The fourth option is incorrect as the maximum number of electrons in an orbital is two (from the Pauli exclusion principle), not eight.

Answer:

When filling orbitals of equal energy, electrons fill them singly first, with parallel spins.