Answer:
5s
Explanation:
The atomic sublevel with the next highest energy after the 4p is 5s.
Based on Aufbau's principle; the sublevels with lower energies are filled up before those with higher energies.
Sublevels do not fill up based on numerical order. The pattern of filling is shown as:
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p
