Cobalt chloride (CoCl₂) exhibits a peak absorbance at approximately 510 nm, which falls within the green region of the visible spectrum.

Here's why:

* Transition Metal Complexes: Cobalt chloride forms complex ions in solution, which are colored due to the absorption of certain wavelengths of light and the transmission of others.

* d-Orbital Transitions: The color arises from the absorption of light that causes electronic transitions between the d-orbitals of the cobalt ion.

* Ligand Field Theory: Ligand field theory explains the splitting of the d-orbitals in the presence of ligands (like chloride ions). This splitting results in specific energy differences, which correspond to the absorption of certain wavelengths of light.

Note: The exact peak absorbance can vary slightly depending on the concentration of the solution and the specific solvent used.