$(a)$ Name the three subatomic particles of an atom.
$(b)$ An atom of an element has $5$ electrons in the $L$ shell.
$(i)$ What is the atomic number of the element?
$(ii)$ State its valency.
$(iii)$ Identify the element and write its name.

(D) The three subatomic particles of an atom are electrons,protons,and neutrons.
$(b) (i)$ The $K$ shell is the first shell and can hold $2$ electrons. The $L$ shell is the second shell and has $5$ electrons. Therefore,the total number of electrons is $2 + 5 = 7$. Since the atom is neutral,the atomic number is equal to the number of electrons,which is $7$.
$(ii)$ The valency is determined by the number of electrons required to complete the octet. Since there are $5$ electrons in the outermost shell ($L$ shell),it needs $3$ more electrons to complete the octet. Thus,its valency is $3$ (or $-3$ as it gains $3$ electrons).
$(iii)$ The element with atomic number $7$ is Nitrogen $(N)$.