The largest radius metal.

The element with the largest atomic radius is cesium.
Atomic radius is defined as the distance between the center of the nucleus and the outermost shell of the atom. Cesium has 6 orbital shells, which means it is automatically large. In addition, it was even believed that the nuclear charge of the nucleus of a cesium atom is high, the attraction force between the nucleus and the outermost electron is low, which makes the electron weakly held (explaining the extreme reactivity of cesium), resulting in an increase in the distance between the outermost electron and the nucleus … When all these factors are combined, the atomic radius of cesium is greatest.