Identify the element with the electron configuration [Xe] 6s^2 4f^14 5d^9.

The electron configuration [Xe] 6s^2 4f^14 5d^9 corresponds to the element Gold (Au). To understand why this is correct, it's essential to break down the electron configuration itself.

Firstly, the [Xe] in the configuration represents the electron configuration of the noble gas Xenon, which accounts for the first 54 electrons. The 6s^2 indicates that there are 2 electrons in the 6s subshell, adding to the total counted so far. The 4f^14 notation signifies that all 14 electrons are present in the 4f subshell, which is characteristic of the lanthanides and helps to fill the electron shells that precede the transition metals.

Lastly, the 5d^9 indicates that there are 9 electrons in the 5d subshell. Gold, with an atomic number of 79, fits this configuration perfectly: starting from Sodium with 11 electrons and adding all the way to Gold includes filling the 5d subshell nearly to completion at 10, while the 4f subshell is fully filled.

Thus, when summarized, the electron configuration [Xe] 6s^2 4f^14 5