Final answer:
The element with the ground-state electron configuration [Ar]4s13d5 is chromium (Cr), as this configuration represents the unique electron arrangement of Cr with a half-filled 3d subshell for added stability.
Step-by-step explanation:
The ground-state electron configuration provided, [Ar]4s13d5, is unique because it shows an exception to the typical filling order of electron orbitals. Typically, the 4s orbital is filled before the 3d, but in this case, there is one electron in the 4s and five in the 3d, which is a characteristic of chromium (Cr). This can be explained by the added stability that results from a half-filled d subshell.
As displayed in the given solution, Cr's electron configuration is indeed [Ar]3d54s1. This is because having a half-filled 3d subshell provides additional stability for this element, which is why Cr has an electron configuration that is not what we might expect based on the aufbau principle.