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Question:

Which one of the following complexes will most likely absorb visible light?

[Sc(H2O)6]3+

[Ti(NH3)6]4+

[V(NH3)6]2+

[Zn(NH3)6]2+

Solution:

For the absorption of light, transition metal should have electrons in d orbital. When we look at the complexes in the options,

[Sc(H2O)6]3+ : Sc3+ has a d0 configuration, so it will not absorb visible light.
[Ti(NH3)6]4+ : Ti4+ has a d0 configuration, so it will not absorb visible light.
[V(NH3)6]2+ : V2+ has a d3 configuration, so it will absorb visible light.
[Zn(NH3)6]2+ : Zn2+ has a d10 configuration, so it will not absorb visible light.

Therefore, [V(NH3)6]2+ will most likely absorb visible light.