Q. Which one of the following ions has electronic configuration [Ar]3d⁶? (At. nos. Mn = 25, Fe = 26, Co = 27, Ni = 28)
A) Co³⁺
B) Ni³⁺
C) Mn³⁺
D) Fe³⁺
Explanation
[Solution from source] Co (Z = 27) is [Ar]3d⁷4s²; removing 3 electrons gives Co³⁺ = [Ar]3d⁶. Fe³⁺ is 3d⁵, Mn³⁺ is 3d⁴ and Ni³⁺ is 3d⁷. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.