If there are only two isotopes, which is most abundant?

Question

Given two isotopes of the same element, are both in the same abundance, is one more than the other, or is there not enough information to decide this?

Answer 1

i don't remember a case where two isotopes were in the same abundance, there is usually a a predominant isotope.

Answer 2

If you know the molar mass of the element (like, H is 1.01, O is 15.999, etc.) then it generally is which ever isotope is closest in molar mass.

So if you're given C-12 and C-14, you know that if they were in equal abundance, your molar mass of C would be something close to 13, if C-14 was more common, then the molar mass of C would be >13, but if C-12 was in a higher abundance, then C would have a molar mass close to 12.

Answer 3

There is not enough information to decide this. There would most likely be a predominant isotope. If you could name the element and the two isotopes, you could mathematically decide which one is more abundant.