18. Which of the following is a diamagnetic material? A) Sodium B) Argon C) Nitrogen D) Oxygen 19. Which of the following is TRUE about paramagnetic atoms? A) They have unpaired electrons. B) They are weakly attracted to magnetic fields. C) A and B are true. D) Neither of these are true. 20. Which rule states that electrons will go to empty orbitals of the same energy before entering into an orbital with an electron present? A) Hand's Rule B) Hund's Rule C) Pauli Exclusion Principle D) Aufbau Principle