20. An atom of which of the following elements has the smallest ionization energy? A. CI C. Si D. S B. P 21. An atom of which of the following elements has the largest second ionization energy? C. Po QBE Q87 A. Cs D. Ba Q88 B. Pb A. Cl (electron affinity -349 kJ/mol) C. O (electron affinity = -141 kJ/mol) 22. Which of the following forms the most stable anion in the gas phase? B. S (electron affinity = -200 kJ/mol) Q89. Q90. Q91. D. C (electron affinity = -122 kJ/mol) 23. According to the building-up principle or Aufbau principle, which subshell is typically filled next after the 5f subshell? Q92. 293. 194. 95. 16. A. 6d B. 4p. C. 7s D. 5s 24. What is the valence-shell electron configuration for the fourth-period element in Group VA? A. 4s25p³ B. 5s25p³ C. 4s24p³ D. 4s23d3 25. The ground-state valence-shell configuration of a particular atom is 4s24p3. This valence shell electron configuration identifies the atom as, A. p-block main-group element B. transition element C. s-block main-group element D. inner transition element 26. All of the following ground-state electron configurations are correct except, A. Fe: [Ar]4s24d6 B. Ca: [Ar]4s2 C. In: [Kr]4d105s25p¹ D. Cu: [Ar]3d104s¹ 27. The ground-state electron configuration of a Mn2+ ion is 1s22s22p63s23p63ds. Therefore, Mn2+ is, A. paramagnetic with five unpaired electrons B. diamagnetic C. paramagnetic with three unpaired electrons D. paramagnetic with two unpaired electrons 28. An atom of which of the following elements has the smallest atomic radius? A. Ge B. Rb C. Ca D. P