Concept of d-orbital and complex compounds

Question

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

(a) !![Sc(H_2O)_6]^(3+)!!

(b) !![Ti(NH_3)_6]^(4+)!!

(c) !![V(NH_3)_6]^(3+)!!

(d) !![Zn(NH_3)_6]^(2+)!!

Solution

All ligands in the option have a zero net charge.

For !!Sc!!, oxidation state is +3 and electron configuration !![Ar],4s^03d^0!!, so electron in d orbital.

For !!Ti!!, oxidation state is +4 and electron configuration !![Ar],4s^03d^0!!, so electron in d orbital.

For !!V!!, oxidation state is +3 and electron configuration !![Ar],4s^03d^2!!, so two unpaired electrons in d orbital.

For !!Zn!!, oxidation state is +3 and electron configuration !![Ar],4s^03d^10!!, so all electrons are paired in d orbital.

Light absorbed by those complexes that have unpaired electron in d orbital.

Therefore, !![V(NH_3)_6]^(3+)!! will absorb the light.

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