Which one of the following ions has electronic configuration[Ar] 3d⁶? (At. no: Mn=25, Fe=26, Co=27, Ni=28)

Options

(a) Ni³⁺
(b) Mn³⁺
(c) Fe³⁺
(d) Co³⁺

Correct Answer:

Co³⁺

Explanation:

Ni³⁺ (28) = [Ar] 3d⁷
Mn³⁺ (25) = [Ar] 3d⁴
Fe³⁺ (26) = [Ar] 3d⁵
Co³⁺ (27) = [Ar] 3d⁶