Identify the element associated with the electron configuration [Xe] 6s² 4f⁹.

The electron configuration [Xe] 6s² 4f⁹ directly indicates that the element has a total of 9 electrons in the 4f subshell alongside 2 in the 6s subshell. When looking at the lanthanide series, where the 4f orbitals are filled, the number of electrons in the 4f subshell determines the specific element.

In this case, the 4f subshell starts filling from Lanthanum (La) with 4f¹ and continues through the series. Terbium (Tb) has an electron configuration of [Xe] 6s² 4f⁹, which matches perfectly with the provided configuration. This means that Terbium is characterized by having 9 electrons in the 4f subshell.

The other elements listed, such as Samarium, Dysprosium, and Thulium, have different numbers of electrons in the 4f subshell. Samarium has 4f⁶, Dysprosium has 4f¹⁰, and Thulium has 4f¹³, making them incompatible with the given electron configuration. Therefore, the correct association of the electron configuration [Xe] 6