Question

Question 3
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) ${}_{15}^{31}X$
(b) ${}_{16}^{31}X$
(c) ${}_{15}^{16}X$
(d) ${}_{16}^{15}X$

Answer 1

The answer is (a).
Given that, number of electrons in element X = 15 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