All of the following complexes will be colored (in the visible) EXCEPT . a) [Zn(en)3]2 b) [Fe(CN)6]4- c) [Ni(H2O)6]2 d) [Cr(NH3)6]3 e) [Cu(NH3)4]2

a

Explanation:

All of the complexes will be colored except [Zn(en)3]2.

Fe, Ni, Cr, and Cu all form colored complexes because of their partially-filled d-orbitals and are generally referred to as transition elements. The d-orbital can split into higher and lower orbitals and electrons can jump from one level to the other. The jumping of electrons leads to light absorption and this characteristic impacts color to elements with partially-filled d-orbitals.

Zinc does not possess a partially-filled d-orbital and as such, its electrons cannot transition between levels, even though it belongs to the 'd-block' element.

The correct option is a.