Answer:
1s2 2s2 2p6 3s2 3p6 3d4 4s2
Explanation:
Cobalt has twenty seven electrons hence Co3+ has twenty four electrons. It has lost three electrons from its valence shell. In filling the orbitals, we keep in mind that the energy of the 4s level is higher than that of the 3s level when a transition metal forms a complex hence the 4s is filled before the 3s level as shown in the answer above.