The configuration of $\text{Fe}(26)$ is—

• a$1s^2 2s^2 2p^6 3s^2 3p^6 3d^6 4s^2$
• b$1s^2 2s^2 2p^6 3s^2 3p^6 3d^7 4s^1$
• c$1s^2 2s^2 2p^6 3s^2 3p^6 3d^8 4s^0$
• d$1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 4p^6$