# Which one of the following ions has electronic configuration $[Ar]3d^6$ <br> (At. nos. Mn = 25, Fe = 26, Co = 27, Ni = 28)
( A ) $Fe^{3+}$
( B ) $Co^{3+}$
( C ) $Mn^{3+}$
( D ) $Ni^{3+}$