Q.Which of the following ions exhibits optical isomerism?

Octahedral tris-chelate complexes such as $[Cr(ox)_3]^{3-}$ are chiral (like a screw) and show optical isomerism.

Optical isomerism arises in coordination compounds when the complex is chiral, i.e. it is non-superimposable on its mirror image, which typically requires the absence of any internal plane of symmetry. This classically happens in octahedral complexes containing three identical symmetric BIDENTATE ligands, $[M(AA)_3]^{n\pm}$, which can exist as non-superimposable left- and right-handed (Δ and Λ) propeller-shaped forms.

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