Homoleptic octahedral complexes of a metal ion '${M^{3+} }$' with three monodentate ligands and $L_1, L_2, L_3$ absorb wavelengths in the region of green, blue and red respectively. The increasing order of the ligand strength is :
Order of $\lambda_{abs} - L_{3 } > L_{1} > L_{2} $ So $ \Delta_{O} $ order will be $ L_{2} > L_{1} >L_{3} \left( \text{as} \Delta_{O} \propto \frac{1}{\lambda_{abs }} \right)$ So order of ligand strength will be $ L_{2} > L_{1} >L_{3}$
A coordination compound holds a central metal atom or ion surrounded by various oppositely charged ions or neutral molecules. These molecules or ions are re-bonded to the metal atom or ion by a coordinate bond.
Coordination entity:
A coordination entity composes of a central metal atom or ion bonded to a fixed number of ions or molecules.
Ligands:
A molecule, ion, or group which is bonded to the metal atom or ion in a complex or coordination compound by a coordinate bond is commonly called a ligand. It may be either neutral, positively, or negatively charged.
