Final answer:
The ground state electron configuration for Ti²⁺ cation is [Ar]3d², as the lower-energy 3d electrons are retained after the higher-energy 4s electrons are removed when forming the ion.
Step-by-step explanation:
The ground state electron configuration for Ti²⁺ is [Ar]3d². Titanium initially has the electron configuration of [Ar]4s²3d² for its neutral atom. When titanium forms a Ti²⁺ ion, the 4s electrons are removed before the 3d electrons due to energy considerations. This results in the electron configuration of [Ar]3d² for the Ti²⁺ cation. This is based on the understanding that, although the 4s orbitals are filled before the 3d orbitals during atomic electron configuration, they are lost first when forming positive ions because the 4s electrons are higher in energy compared to the 3d electrons as the d orbitals are filled. Hence, the correct answer is option (d).