9. Na+ has completely filled K and L shells. Explain.

A sodium atom has 11 electrons in its orbits, hence its atomic number is also 11 and has the same number of protons and electrons. Thus, its electronic configuration is K-2; L-8; M-1; The one electron in the M shell is lost and it obtains a positive charge since it has one more proton than the electrons, and obtains a positive charge, Na+. Now, the configuration is K-1; L-8 and it is a filled state. Hence, it is very stable so it is difficult to remove the electron from a filled state.