Identify the element with the electron configuration [Ar] 4s² 3d³.

The electron configuration [Ar] 4s² 3d³ corresponds to an element with a total of 23 electrons. In this configuration, the notation indicates that there are two electrons in the 4s subshell and three electrons in the 3d subshell.

Counting the electrons, we start with the noble gas argon (Ar), which has 18 electrons. Adding the two electrons in the 4s subshell brings the total to 20, and adding the three electrons in the 3d subshell gives us 23 electrons in total. The element with 23 electrons is vanadium (V), which is located in period 4 and group 5 of the periodic table.

This configuration is particularly important in understanding the transition metals and how they fill their d orbitals. In vanadium, the 3d subshell is being populated, which is a characteristic feature of transition metals, leading to unique properties such as variable oxidation states and colored compounds.

In summary, the electron configuration [Ar] 4s² 3d³ uniquely identifies vanadium as it corresponds to the distribution of electrons in this element, reflecting its position in the periodic table.