Linked from
The 10 pages that link to Isotopic abundance, each with the reason it gives.
BoronRelated: Natural boron’s isotope ratio varies and affects its measured atomic mass.
DeuteriumRelated: Deuterium is rare in natural hydrogen compared with protium.
Atomic weightRelated: Abundance determines how strongly each isotope’s mass affects the average.
ProtiumRelated: Protium’s dominance is expressed as its high natural isotopic abundance.