What is the heaviest element that has only one isotope and is not radioactive?
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.
To find the answer to this question, we need to consider the heaviest naturally occurring element that has only one stable isotope and is not radioactive.
First, we can identify the naturally occurring elements that have only one stable isotope. These include elements like hydrogen (H-1), helium (He-4), lithium (Li-7), beryllium (Be-9), boron (B-11), fluorine (F-19), and phosphorus (P-31), among others.
Next, we need to determine which of these elements is the heaviest. The atomic number of an element corresponds to the number of protons in its nucleus, so we can compare the atomic numbers of the elements to determine their relative order.
Among the elements listed above, phosphorus (P) has the highest atomic number at 15. Therefore, phosphorus is the heaviest naturally occurring element (with only one stable isotope) that is not radioactive.
In conclusion, the heaviest element that has only one isotope and is not radioactive is phosphorus (P).