the element with the largest atomic number that is believed to have a stable nucleus is Oganesson, with the atomic number 118. Oganesson (symbol Og) is a synthetic element that was first synthesized in 2002 by a team of Russian and American scientists. It is a member of the noble gases group and is located in period 7 of the periodic table.
Due to its high atomic number and the challenges associated with synthesizing and studying superheavy elements, the stability of oganesson's nucleus is not yet fully understood. However, based on theoretical predictions and limited experimental data, it is thought to have a relatively long enough half-life to be considered a "stable" element.
It's important to note that the field of superheavy element research is still evolving, and new discoveries and advancements may lead to changes in our understanding of the stability of nuclei at extreme atomic numbers. Therefore, it's always a good idea to consult up-to-date scientific literature for the latest information on this topic.