Which element although situated outside the Radioactive series, has radioactive isotope ?

Classical natural radioactive decay series (such as the Thorium, Actinium, or Uranium series) feature heavy elements with very high atomic numbers (e.g., Radium, Polonium, Uranium).
However, many lighter main-group elements situated outside these default radioactive series possess highly prominent radioactive isotopes:

1. Fluorine has the artificial radioisotope $\text{F-18}$ (highly valuable in medical PET scanning).
2. Iodine has notable radioisotopes like $\text{I-131}$ and $\text{I-129}$ used extensively in thyroid tracking and medical therapies.
3. Chlorine has the long-lived cosmogenic radioisotope $\text{Cl-36}$.

As all these elements have recognized radioactive isotopes while sitting outside the traditional heavy actinide/decay pathways, the answer is "All of the above".