What is the heaviest element that has only one isotope and is not radioactive?

Answer 1

I am uncertain what you mean by one isotope...do you mean one NATURALLY occuring isotope?
OR, fo you mean has only one stable isotope, but can have other radioactive isotopes?

Which ever it is, here is the answer in the bottom chart.
http://en.wikipedia.org/wiki/Stable_isotope


I suspect this is what you seek.
http://en.wikipedia.org/wiki/Stable_isotope
But the wording of the question makes me wonder.