Which of the following configuration is correct for iron?

Options

A. `1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^7`
B. `1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^5`
C. `1s^2 2s^2 2p^6 3s^2 3p^6 3d^5`
D. `1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^6`

Answer

D