Choose an example of an energy level diagram for an element and use it to explain the Aufbau principle, Hund's rule, and the Pauli exclusion principle.

Which best describes the present-day universe? opaque, expanding very slowly, stars produce heavy elements transparent, expanding at an accelerated rate, stars produce heavy elements opaque, expanding at an accelerated rate, stars produce only hydrogen and helium transparent, expanding very slowly, stars produce only hydrogen and helium