An atom of an element has $2$ electrons in the $M$ shell, i.e., the third shell. What will be the atomic number of this element? Name this element. Find the valency of this element. Also, find the number of neutrons in the atom of this element (assume mass number is $24$).

(D) $(i)$ The electronic configuration is $K=2, L=8, M=2$. The total number of electrons is $2 + 8 + 2 = 12$. Therefore, the atomic number is $12$.
$(ii)$ The element with atomic number $12$ is Magnesium $(Mg)$.
$(iii)$ Since it has $2$ electrons in its outermost shell, it loses $2$ electrons to achieve a stable octet. Thus, its valency is $2$.
$(iv)$ The number of neutrons is calculated as: $\text{Number of neutrons} = \text{Mass number} - \text{Atomic number} = 24 - 12 = 12$.