Name the element which has:
$(a)$ the electronic configuration $2, 8, 1$.
$(b)$ a total of two shells,with $4$ electrons in the valence shell.
$(c)$ a total of three shells,with $3$ electrons in the valence shell.
$(d)$ one shell which is completely filled with electrons.
$(e)$ twice as many electrons in the second shell as in the first shell.

(N/A) Sodium $(Na)$ has the electronic configuration $2, 8, 1$.
$(b)$ Carbon $(C)$ has atomic number $6$. Its electronic configuration is $2, 4$. It has a total of two shells ($K$ and $L$),with $4$ electrons in the valence shell.
$(c)$ Aluminium $(Al)$ has atomic number $13$. Its electronic configuration is $2, 8, 3$. It has a total of three shells ($K, L,$ and $M$),with $3$ electrons in the valence shell.
$(d)$ Helium $(He)$ has atomic number $2$. Its electronic configuration is $2$. It has one shell $(K)$ which is completely filled with $2$ electrons.
$(e)$ Carbon $(C)$ has atomic number $6$. Its electronic configuration is $2, 4$. The first shell $(K)$ has $2$ electrons and the second shell $(L)$ has $4$ electrons. Thus,it has twice as many electrons in the second shell as in the first shell.