Question

Na has completely filled K and L shells. Explain.

Answer 1

Sodium atom (Na), has atomic number =11
Number of protons =11
Number of electrons = 11
Electronic configuration of Na = K, L, M — 2, 8, 1

Sodium atom (Na) looses 1 electron to become stable and form $N{a}^{+1}$ ion.
Electronic configuration of $N{a}^{+1}$ ion is: K, L — 2, 8
Hence it has completely filled K and L shells.