Question

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

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

Answer 1

The correct option is A

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

Given that, number of electrons in element X = 15 and number of neutrons = 16

Atomic number = number of protons = number of electrons in neutral atom = 15

Mass number = number of protons + number of neutrons = 15 + 16 = 31

Thus, the atom is represented as ${}_{15}^{31}\text{X}$.