Which of the following ions has electronic configuration [Ar]3d6? (At. nos. Mn = 25, Fe = 26, Co = 27, Ni = 28)
- Ni3+
- Mn3+
- Fe3+
- Co3+
Answer
(4) Co3+
Solution
Electrons are removed first from 4s and then from 3d.
Ni3+: 28 - 3 = 25 electrons [Ar] 3d7
Mn3+: 25 - 3 = 22 electrons [Ar] 3d4
Fe3+: 26 - 3 = 23 electrons [Ar] 3d5
Co3+: 27 - 3 = 24 electrons [Ar] 3d6
Answer: (4)