What element corresponds to the electron configuration [Rn] 7s^2?

The electron configuration [Rn] 7s^2 indicates that the element in question has a complete set of electrons equivalent to Radon (Rn), which is a noble gas, followed by two additional electrons in the 7s subshell. This is characteristic of the alkaline earth metals, which typically have two electrons in the outermost s subshell.

In this case, when we look at the periodic table, we find that the element with this configuration is Radium (Ra), which is located in Group 2 (the alkaline earth metals) and Period 7. Radium has atomic number 88, and its electron configuration confirms that it indeed has two electrons in the 7s subshell after the Radon core.

The other elements listed do not have this configuration; for example, Radon itself ends with [Rn], while Polonium (Po) and Bismuth (Bi) have lower principal energy levels and therefore will not end with 7s^2. Thus, the configuration you provided perfectly matches that of Radium.