There are a total of eight completely filled sublevels in Krypton in its ground states. These sublevels are:
1s, 2s, 2p, 3s, 3p, 3d, 4s and 4p
This configuration indicates that Krypton is stable as it does not need to gain or lose any electrons to complete its octet. This is why Krypton is a noble gas.
