Question

Which one of the following complexes will most likely absorb visible light?
[Atomic numbers: $Sc=21,Ti=22,V=23,Zn=30$]

• A. $\left[Sc\right(H_{2}O{)}_6{]}^{3+}$
• B. $\left[Ti\right(N{H}_3{)}_6{]}^{4+}$
• C. $\left[V\right(N{H}_3{)}_6{]}^{2+}$
• D. $\left[Zn\right(N{H}_3{)}_6{]}^{2+}$

Answer 1

Answer: (C)

$\left[V\right(N{H}_3{)}_6{]}^{2+}$

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

A) $S{c}^{3+}$ - no electrons in d orbital. So, $S{c}^{3+}$ doesn't absorb light.

B) $T{i}^{4+}$ - no electrons in d orbital. So, $T{i}^{4+}$ doesn't absorb light.

C) $V^{2+}$ - three electrons in d orbital. So, $V^{2+}$ absorbs light.

D) $Z{n}^{2+}$ - no empty d orbitals, electrons in d orbitals are filled. So, $Z{n}^{2+}$ doesn't absorb light, so transitions cannot happen.