The ion of an element has $3$ positive charges. The mass number of the atom is $27$ and the number of neutrons is $14$. What is the number of electrons in the ion?

Calculate the number of neutrons present in the nucleus of an element $X$ which is represented as $^{31}_{15}X$.

Two elements are denoted as follows:
$_{20}^{40}A$ and $_{18}^{40}B$
$(a)$ Find the number of electrons present in $A$ and $B$.
$(b)$ Find the number of nucleons present in $A$ and $B$.
$(c)$ Explain the special 'term' used to represent $A$ and $B$ and define the same.

Complete the following table.

Atomic Number	Mass Number	Number of Neutrons	Number of Protons	Number of Electrons	Name of the Atomic Species
$9$	-	$10$	-	-	-
$16$	$32$	-	-	-	sulphur
-	$24$	-	$12$	-	-
-	$2$	-	$1$	-	-
-	$1$	$0$	$1$	$0$	-

Give a reason to explain why
$(a)$ isotopes of an element show identical chemical properties?
$(b)$ the atomic masses of elements are in fractions?
$(c)$ atoms combine with other atoms?

Which property of an element can be used for its identification?