Which of the following coordination entities should be expected to absorb light of lowest frequency?

Options

A. `[Cr(en)_(3)]^(2+)`
B. `[CrCl_(6)]^(3-)`
C. `[Cr(NH_(3))_(6)]^(3+)`
D. `[Cr(CN)_(6))]^(3-)`

Answer

B

Explanation

The coordination entitiy, for which crystal field splitting is smaller, absorbs light of losed frequency. Weaker the ligand field strength, smaller will be the crystal field splitting. The order of field strength of varisous ligands is as `CN^(-)gt en gt NH_(3) gt Cl^(-)`
Hence, `[CrCl_(6)]^(3-)` due to the presence of `Cl^(-)` ligand abosrbs light of lowest frequency.