Question

Which one of the following ions has electronic configuration $\left[\right.Ar\left]\right.3d^{6}$ ?
(At. nos. Mn = 25, Fe = 26, Co = 27, Ni = 28)

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

Answer 1

Answer: (A)

In case of $Co^{+ 3}\left[\right.Ar\left]\right.3d^{6}$ configuration is possible $_{27}Co \rightarrow \left[\right.Ar\left]\right.3d^{7}4s^{2}$
On removing $3e^{-}$ we get $Co^{3 +} \rightarrow \left[\right.Ar\left]\right.3d^{6}$