The following data represents the distribution of electrons,protons,and neutrons in atoms of four elements $A, B, C, D.$

Element	Protons,Neutrons,Electrons
$A$	$9, 10, 9$
$B$	$16, 16, 16$
$C$	$12, 12, 12$
$D$	$17, 22, 17$

Answer the following questions:
$(a)$ Give the electronic distribution of element $B.$
$(b)$ The valency of element $A$.
$(c)$ The atomic number of element $B.$
$(d)$ The mass number of element $D$.

(N/A) The atomic number of element $B$ is $16$. Its electronic configuration is $2, 8, 6$.
$(b)$ The atomic number of element $A$ is $9$. Its electronic configuration is $2, 7$. To complete its octet,it gains $1$ electron. Therefore,its valency is $1$.
$(c)$ The atomic number of an element is equal to the number of protons in its nucleus. For element $B$,the number of protons is $16$,so its atomic number is $16$.
$(d)$ The mass number of an element is the sum of the number of protons and neutrons. For element $D$,mass number $= 17 + 22 = 39$.