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 correct option is (A).

Explanation of the correct option:

Step 1- Calculation of the mass number and an atomic number of element X.

Number of protons =Number of electrons=15

Number of neutrons= 16

Mass Number = Number of protons + Number of neutrons

= 15+16 =31

Atomic number = Number of protons of the element = 15

Step 2- Representation of an element

The mass number is written on the upper side and the atomic number is written on the lower side of the element.

${}_{\mathrm{atomic}\mathrm{number}}{}^{\mathrm{mass}\mathrm{number}}\mathrm{X}$

Hence, the correct representation of element X that has 15 electrons and 16 neutrons is option (A) ${}_{15}{}^{31}\mathrm{X}$.