Which element has:
$(a)$ two shells,both of which are completely filled with electrons?
$(b)$ the electronic configuration $2, 8, 2$?

(N/A) Neon $(Ne)$ has two shells,$K$ and $L$,both of which are completely filled with electrons ($2$ electrons in $K$ shell and $8$ electrons in $L$ shell,total $10$ electrons).
$(b)$ Magnesium $(Mg)$ has the electronic configuration $2, 8, 2$ (total $12$ electrons).