Which element has
$(a)$ a total of three shells,with four electrons in its valence shell?
$(b)$ a total of two shells,with three electrons in its valence shell?
$(c)$ twice as many electrons in its second shell as in its first shell?

(N/A) Silicon $(Si)$ has a total of three shells,with four electrons in its valence shell ($2$ electrons in $K$ shell,$8$ electrons in $L$ shell,and $4$ electrons in $M$ shell).
$(b)$ Boron $(B)$ has a total of two shells,with three electrons in its valence shell ($2$ electrons in $K$ shell and $3$ electrons in $L$ shell).
$(c)$ Carbon $(C)$ has twice as many electrons in its second shell as in its first shell ($2$ electrons in $K$ shell and $4$ electrons in $L$ shell).