Explanation:
Na represents the neutral element; Sodium. Because of it's atomic number of 11, It has 11 electrons.
Na+ on the other hand represents a cation. The sodium ion has lost an electron, hence the total number of electrons it has = 10.
The K and L shells each have maximum number of electrons they can accommodate. This is given by the formular; 2n^2
K shell = 2 (1)^2 = 2 electrons
L shell = 2 (2)^2 = 8 electrons
Seeing as Na+ has 10 electrons, It completely filled the K and L shells ( 2 + 8 = 10 )
