Question

Which is the most abundant oxygen isotope?

Answer 1

Well, clearly `""^16O` will be the most abundant isotope.

Explanation:

The quoted atomic mass is the WEIGHTED average of the individual isotopic masses, with the weighting determined by the isotopic abundance. The `15.9994" amu"` mass is close to the mass of `""^16O`, which argues that `""^16O` is present in overwhelming abundance.

You will have to look up the proportions of the individual isotopes yourself.