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

(b) ${}_{16}{}^{31}\mathrm{X}$

(c) ${}_{15}{}^{16}\mathrm{X}$

(d) ${}_{16}{}^{15}\mathrm{X}$

Answer 1

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

In an atom, the number of electrons is equal to number of protons ,which in turn is equal to the atomic number of the element. Also, the sum of number of protons and neutrons represents the mass number of the element. Therefore, the correct option is (a).