[Xe] 6s² 5d¹

Here's how to understand this:

* [Xe] represents the electron configuration of Xenon (Xe), the noble gas that comes before Lanthanum on the periodic table.

* 6s² indicates that there are two electrons in the 6s orbital.

* 5d¹ indicates that there is one electron in the 5d orbital.

This means that the Lanthanum atom has the same electron configuration as Xenon, plus two additional electrons in the 6s orbital and one in the 5d orbital.