Đáp án:

Cấu hình electron:

$Cu: 1s^2$ $2s^2$ $2p^6$ $3s^2$ $3p^6$ $3d^{10}$ $4s^1$ 

$S^{2-}$: $1s^2$ $2s^2$ $2p^6$ $3s^2$ $3p^6$

$Fe^{2+}$: $1s^2$ $2s^2$ $2p^6$ $3s^2$ $3p^6$ $3d^6$ 

$Fe^{3+}$: $1s^2$ $2s^2$ $2p^6$ $3s^2$ $3p^6$ $3d^5$ 

$Cr^{3+}$: $1s^2$ $2s^2$ $2p^6$ $3s^2$ $3p^6$ $3d^3$ 

$Cu^{2+}$: $1s^2$ $2s^2$ $2p^6$ $3s^2$ $3p^6$ $3d^9$

Ô lượng tử: (như hình)