What may be the stable oxidation state of the transition element with the following d-electron configuration in the ground state of their atoms `3d^3, 3d^5, 3d^8, and 3d^4` ?

Explanation

Stable oxidation states:
`3d^3 ` : Chormium `(3d^3 4s^2)` : oxidation states +2, +3, + 4 and +5
`3d^5` : Manganese `(3d^5 4s^1)` : oxidation states +3, + 4, and +6.
`3d^5` : Manganese `(3d^5 4s^2)`: oxidation states (+2, + 4, + 6, + 7).
`3d^8` : Cobalt `(3d^7 4s^2)`: oxidation states + 2, + 3 (in complexes) (Co belongs to 9 group)
`3d^4` : such configuration does not exist in ground state .