## Chemistry and Chemical Reactivity (9th Edition)

a) Fe, group 8, period 4 $[Ar]\ 3d^6\ 4s^2$ $Fe^{2+}: [Ar]\ 3d^6$ $Fe^{3+}: [Ar]\ 3d^5$ b) $Co^{2+}, Al^{3+}, Sn^{4+}$ Co, group 9, period 4 $[Ar]\ 3d^7\ 4s^2$ $Co^{2+}: [Ar]\ 3d^7$, paramagnetic, three unpaired electrons. Al, group 13, period 3 $[Ne]\ 3s^2\ 3p^1$ $Al^{3+}: [Ne]$, diamagnetic Sn, group 14, period 5 $[Kr]\ 4d^{10}\ 5s^2\ 5p^2$ $Sn^{4+}: [Kr]\ 4d^{10}$, diamagnetic