Which of the following represents the ground-state electron configuration of a stable transition metal ion that contains exactly three unpaired electrons?
[Ar]4s23d3\text{[Ar]} 4\text{s}^2 3\text{d}^3[Ar]4s23d3
[Ar]3d3\text{[Ar]} 3\text{d}^3[Ar]3d3
[Ar]4s13d2\text{[Ar]} 4\text{s}^1 3\text{d}^2[Ar]4s13d2
[Ar]3d6\text{[Ar]} 3\text{d}^6[Ar]3d6
