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[Ti(H2O)6]2+ would present the least intense peaks in the UV-Vis spectrum. This is because titanium(II) is a d0 ion, meaning it has no d electrons to participate in d-d transitions, which are responsible for the absorption of visible light and the appearance of color in coordination complexes. The other ions have d electrons and would exhibit more intense peaks in the UV-Vis spectrum due to d-d transitions.