1. Radioactive elements are those whose nuclei are unstable and spontaneously decay, emitting radiation.
2. Astatine (At, element 85) is a highly radioactive halogen. All its isotopes are short-lived.
3. Francium (Fr, element 87) is a highly radioactive alkali metal. All its isotopes are short-lived.
4. Tritium (Hydrogen-3) is a radioactive isotope of hydrogen.
5. Zirconium (Zr, element 40) is a transition metal. While it has some radioactive isotopes, naturally occurring zirconium is composed primarily of stable isotopes and is NOT generally considered a radioactive element in its common form.