An atom of an element has fourth shell as the valence shell. The difference between electrons present in L- and M-, K-, and N-shells are $1 \mathrm{and} 0$, respectively. Find the atomic number of that element.

Write down the 

(a) electronic configuration

(b) number of valence electrons

(c) number of neutrons and 

(d) nature of the element

for ${}_6\mathrm{X}^{12}$.

Write down the 

(a) electronic configuration

(b) number of valence electrons

(c) number of neutrons and 

(d) nature of the element

for ${}_{10}\mathrm{Y}^{20}$.

Write down the 

(a) electronic configuration

(b) number of valence electrons

(c) number of neutrons and 

(d) nature of the element

for ${}_{19}\mathrm{Z}^{39}$