What species has the electron configuration [ar]3d2?

The electronic configuration of the Argon (Ar) has atomic number 18 with all its layers filled

To fill the 3d2 level, you must first fill the 4s level with its two electrons, since it has less energy so the electronic configuration of the atom would be

[Ar] 4s² 3d² corresponding to Titanium

The given configuration is : [Ar]3d²

The inner shells of this species has the noble gas, Argon (Ar) configuration while its valence configuration is 3d².

Now the atomic number of Argon = 18

Therefore, the species will have an atomic number = 18 + 2 = 20

Based on the periodic table the species with atomic number 20 is calcium

Ca = [Ar] 3d²