What element has the electron configuration [Xe] 6s¹?

The electron configuration [Xe] 6s¹ indicates that the element in question has the noble gas xenon as its core configuration, followed by one additional electron in the 6s subshell. This configuration specifies that there is one electron in the outermost energy level, which corresponds to the alkali metals group.

Looking at the options provided, cesium (Cs) is known to have an electron configuration of [Xe] 6s¹, identifying it as an alkali metal. Alkali metals are characterized by having one electron in their outermost shell, which corresponds to the s subshell of their highest energy level. This group includes lithium, sodium, potassium, rubidium, cesium, and francium.

The other elements listed do not fit this electron configuration. Barium (Ba) has a configuration of [Xe] 6s², indicating two electrons in the 6s subshell, while tantalum (Ta) and tungsten (W) are transition metals with more complex configurations that involve d orbitals, namely [Xe] 4f¹⁴ 5d³ 6s² for tantalum and [Xe] 4f¹⁴ 5d⁴ 6s²