Question

Which of the following complex ions is not expected to absorb visible light?

Options

• [Ni(CN)₄]²⁻

• [Cr(NH₃)₆]³⁺

• [Fe(H₂O)₆]²⁺

• [Ni(H₂O)₆]²⁺

Answer 1

[Ni(CN)₄]²⁻

Explanation:

The complex [Ni(CN)₄]²⁻ is not expected to absorb visible light because cyanide (CN⁻) is a strong field ligand, which causes a large splitting of the d-orbitals. This large splitting means the energy gap between the orbitals is too big for visible light to excite electrons, so it absorbs in the ultraviolet region instead.