Solution

Only those transition metal complexes are expected to absorb visible light, in which d- subshell is incomplete and excitation of an electron from a lower energy orbital to higher energy orbital is possible.

(a) In $$\left[ Sc({ H }_{ 2 }O)({ NH }_{ 3 })_{ 3 } \right] ^{ 3+ }$$ Sc is present in $$ { Sc }^{ 3+ }$$=$$[Ar]3{ d }^{ 0 },4{ s }^{ 0 }$$

Since in this complex excitation of the electron is not possible, it will not absorb visible light.

(b) $$\left[ Ti(en)_{ 2 }(N{ H }_{ 3 })_{ 2 } \right] ^{ 4+ },$$ Ti is present as $${ Ti }^{ 4+ }$$

$${ Ti }^{ 4+ }=[Ar]3{ d }^{ 0 },4{ s }^{ 0 }$$
Hence it will not absorb visible light

(c) In $$\left[ Cr({ NH }_{ 3 })_{ 6 } \right] ^{ 3+ }$$ Cr is present as $${ Cr }^{ 3+ }$$

$${ Cr }^{ 3+ }$$=$$[Ar]3{ d }^{ 3 },4{ s }^{ 0 }$$

Since this complex has three unpaired electrons excitation of electrons is possible and thus, it is expected that this complex will absorb visible light.

(d) In $$\left[ Zn(N{ H }_{ 3 })_{ 6 } \right] ^{ 2+ }$$ Zn is present as $${ Zn }^{ 2+ }$$

$${ Zn }^{ 2+ }$$=$$[Ar]3{ d }^{ 10 },4{ s }^{ 0 }$$

Hence , this complex will not absorb visible light.

The correct option is C.