Question

Which one of the following ions has electronic configuration $[Ar] 3d^6 ?$ (At.no. $Mn =25, Fe = 26,Co =27, Ni = 28)$

• A. $Ni^{3+}$
• B. $Mn^{3+}$
• C. $Fe^{3+}$
• D. $Co^{3+}$

Answer 1

Answer: (D)

$Co^{3+}$

Answer 2

$Ni^{3+}(28)=[Ar]3d^7$ $Mn^{3+}(25)=[Ar]3d^4$ $Fe^{3+}(26)=[Ar]3d^5$ $Co^{3+}(27)=[Ar]3d^6$ Hence, $Co^{3+}$ has $3d^6$ electronic configuration