Question

The number of electrons in an element X is $15$ and the number of neutrons is $16$. Which of the following is the correct representation of the element?

• A. ${}_{15}{}^{31}\mathrm{X}$
• B. ${}_{16}{}^{31}\mathrm{X}$
• C. ${}_{15}{}^{16}\mathrm{X}$
• D. ${}_{16}{}^{15}\mathrm{X}$

Answer 1

The correct option is A

${}_{15}{}^{31}\mathrm{X}$

The explanation for the correct option

(A)${}_{15}{}^{31}\mathrm{X}$

Atomic number

• $\text{Atomic number}\left(\text{Z}\right)\text{= number of protons in the nucleus of an atom = number of electrons in a neutral atom}$
• So, the atomic number of a given element is $15$.

Mass number

• $\text{Mass number}\left(A\right)\text{=Number of neutron +Number of protons}$
• $$\begin{gathered} \text{Mass number=15+16} \\ =31 \end{gathered}$$

Representation of element

• Element is represented as ${\mathrm{X}}_{\mathrm{Z}}^{\text{A}}$.
• So, the representation of element is ${\mathrm{X}}_{15}^{31}$.

The explanation for the incorrect option

• The representation of element is ${\mathrm{X}}_{15}^{31}$. Hence, options (B), (C), and (D) are incorrect.

Hence, option (A) is correct. The representation of element is ${\mathrm{X}}_{15}^{31}$.