Which element has the electron configuration [Rn] 7s^1?

The electron configuration [Rn] 7s^1 indicates that the element has a total of 86 electrons (from the radon core) plus one additional electron in the 7s orbital. This configuration corresponds to an element located in the seventh period of the periodic table, specifically in group 1, which contains the alkali metals.

Francium, being the only element that fits this configuration, is located in group 1 and is known for having a single electron in its outermost s orbital (the 7s orbital in this case). This characteristic is typical of alkali metals, which exhibit similar properties due to having one electron in their outermost shell.

The other elements listed do not have this specific electron configuration. Cesium (Cs) has the configuration [Xe] 6s^1, which accounts for its placement in the sixth period. Potassium (K) and Sodium (Na) also fall into periods four and three, respectively, with configurations that end with 4s^1 and 3s^1. Thus, only Francium has the configuration that corresponds with [Rn] 7s^1.