I think it is because most of the settlements in Australia are under the Spanish rule. Aside from that, Australia was part of the Spanish territory because of the papal bull mandated by Pope Alexander VI. The papal bull divided the world between Spain and Portugal. Spain has full control of the west while Portugal owns the east side of the world
Portuguese explorers were forced to study Australia in secret.
An isotope is an atom with a different number of neutrons than another atom of the same element. Since atoms of the same element all have the same number of protons, choice B(6pro &6neu vs. 6pro&7neu) is an example of isotopes