Use electron configurations to explain the following observations:
(a) The first ionization energy of phosphorus is greater than that of sulfur.
(b) The electron affinity of nitrogen is lower (less negative) than those of both carbon and oxygen.
(c) The second ionization energy of oxygen is greater than the first ionization energy of fluorine.
(d) The third ionization energy of manganese is greater than those of both chromium and iron.