Zirconium is a chemical element with the symbol Zr and atomic number 40. It is a transition metal commonly used in various applications, including nuclear reactors and the production of alloys. While some isotopes of zirconium are radioactive, the most abundant and naturally occurring isotope, Zirconium-90 (Zr-90), is stable.
Stable isotopes do not undergo radioactive decay, meaning they do not spontaneously emit radiation or decay into other elements over time. Zirconium-90 has a stable nucleus and does not exhibit any radioactive properties.
In contrast, Astatine (At), Francium (Fr), and Tritium (H-3) are all radioactive isotopes. Astatine is a highly radioactive element, Francium is the most unstable of the naturally occurring elements, and Tritium is a radioactive isotope of hydrogen.
Therefore, of the options provided, Zirconium is the element that is not radioactive.