Question

If an isotope of ‘H’ has a mass number =3, how many neutrons does it have?

Answer 1

Atomic mass number:

• The mass number(A) is the total number of neutrons(n) and protons(p) present in a nucleus of an atom.
• Atomic mass number = Protons + Neutrons

Isotopes:

• Isotopes are the species of the same element which have the same atomic number but differ in mass number.

Explanation of Neutrons in an isotope of tritium:

• There are three isotopes of hydrogen species; Protium (${\mathrm{H}}_1^1$), Deuterium (${\mathrm{H}}_1^2$ ), and Tritium (${\mathrm{H}}_1^3$) which have the same atomic number 1 (number of proton = 1) but differ in mass number or differ in the number of neutrons.

Finding the number of neutrons in an isotope of ‘H’ has a mass number of 3:

• Formula: Number of neutrons = Atomic mass number - Atomic number
• Number of neutrons in tritium = 3 - 1 = 2
• Tritium (${\mathrm{H}}_1^3$) is an isotope of hydrogen species that contains one proton and two neutrons and the number of electrons in a neutral atom or species is equal to the number of protons.

Therefore a number of neutrons(n) in tritium having mass number three is equal to 2.