The electron configuration of _{25}Mn at the ground state is ….
a. 1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^6
b. 1s^2 2s^2 2p^6 3s^2 3p^3 4s^2 3d^8
c. 1s^2 2s^2 2p^6 3s^2 3p^3 4s^1 3d^9
d. 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^5
e. 1s^2 2s^2 2p^6 3s^2 3p^6 4s^0 3d^7