B. Iron has an atomic number of 26. Therefore, Fe2+
has 24 electrons and Fe3+
has 23 electrons. An atom, or ion, with an odd number of electrons cannot be diamagnetic (all electrons paired). For this reason, choices B and C are eliminated. Since iron is filling a d subshell, it has five orbitals to fill before it will electron pair. Fe2+
has six electrons past the nearest noble gas configuration. It is irrelevant whether two of these electrons are paired in the 4s orbital, or one elctron is in the 4s orbital, or no electrons are in the 4s orbital. In any case, the remaining 4, 5, 6 electrons, respectively, will not all pair in the 3d orbitals. Therefore, Fe2+
is paramagnetic, and the answer must be D.
(this multiple choice question has been scrambled)