The element with the highest level of radioactivity among the 118 known elements is not a fixed characteristic, as it depends on various factors, including the specific isotope of an element and its decay properties. Different isotopes of elements have different half-lives and decay modes, which determine their level of radioactivity.
That being said, among the naturally occurring elements, polonium (Po) is one of the most radioactive. Polonium-210 (210Po) is particularly notable for its high level of radioactivity. It is an alpha emitter and has a half-life of about 138 days. Polonium-210 is highly toxic and poses a significant health risk if ingested or inhaled.
However, it's worth mentioning that there are artificially created elements beyond atomic number 118 (oganesson) that have been synthesized in laboratories. These superheavy elements, such as elements 119 and beyond, are highly unstable and have very short half-lives, making them extremely radioactive. These elements are typically produced through nuclear reactions and quickly decay into other elements. The study of superheavy elements is an active area of research in nuclear physics.