Question

What is the relative abundance of an isotope?

Answer 1

Every element in the periodic table has an atomic number and mass number. Atomic number gives the number of protons and mass number gives the sum of the number of the protons and neutrons. An element with the same atomic number but with a different mass number can be called an isotope. The relative amounts in which each isotope is present in an element is known as relative abundance.

Complete answer:
Atoms are tiny particles consisting of three types of subatomic particles namely electron, proton and neutron. Proton is a positively charged particle, neutrons are not charged and an electron is a negatively charged particle.
Each element in the periodic table has its own atomic number and mass number. Atomic number gives the number of protons and mass number gives the sum of the number of the protons and neutrons. An element with the same atomic number but with a different mass number can be called an isotope.
Hydrogen can exist in three isotopic forms namely proton, deuterium and tritium. The relative amounts in which each isotope is present in an element is known as relative abundance.
The relative abundance of protons is $99.9\%$ and the deuterium has $0.01\%$ of relative abundance, whereas the tritium can occur as traces only.

Note:
The most commonly occurring isotope is proton which has $99.9\%$ availability in nature. Due to the availability and NMR-active it can be used as reference and isotopic labelling. $^{13}C$ can also be used as isotopic labelling. Isotopes have so many applications in treatment of cancer.