The reactivity order of the group 1 metal ions based on their electronic configuration can be determined by examining the ease with which they lose their outermost electron to form a positive ion. As we move down the group in the periodic table, the atomic size increases, and the outermost electron is further away from the nucleus. This results in a weaker attraction between the nucleus and the outermost electron, making it easier for the atom to lose that electron and become more reactive.Based on this, the reactivity order of the group 1 metal ions is:Cs+ > K+ > Na+ > Li+Cesium Cs+ is the most reactive, followed by potassium K+ , sodium Na+ , and lithium Li+ being the least reactive among the given metal ions.