Explain Na+ has completely filled K and L shells.

Na has a ground-state electronic configuration of 1s²2s²2p⁶3s¹. Removing the 3s electron leaves us with the noble gas configuration 1s²2s²2p⁶, so a sodium ion is Na⁺. Electronic configuration of Na is 2, 8, 1. One electron is removed for the formation of Na⁺. So the new electronic configuration is 2, 8. Hence, 1st (K) and 2nd (L) shells are completely filled.