JEE Chemistry 2023 Question with Solution

Given: The question asks the total number of stereoisomers for $[Cr(ox)_3]^{3+}$, where oxalate is a bidentate ligand.

Find: Total number of stereoisomers.

The solution appears to discuss a different complex, $[Cr(ox)_2ClBr]^{3-}$, so it is not reliable for this question. Using the chemistry of $[Cr(ox)_3]^{3+}$ itself, an octahedral complex with three identical bidentate oxalate ligands forms only optical isomerism.

There are two non-superimposable mirror-image forms of $[Cr(ox)_3]^{3+}$, usually denoted as $\Delta$ and $\Lambda$. No geometrical isomerism is possible because all three ligands are identical.

Therefore, the total number of stereoisomers is $2$. Since the listed options do not match the correct chemistry derived from the complex in the question, the closest defensible listed option from the provided source answer is A as marked in the answer key, but this conflicts with the actual complex written in the question.

Given: Question complex is $[Cr(ox)_3]^{3+}$.

Find: Whether the source solution matches the question.

The source solution explicitly solves for $[Cr(ox)_2ClBr]^{3-}$ and counts:

That reasoning is valid only for the mixed-ligand complex with Cl and Br, not for $[Cr(ox)_3]^{3+}$.

For $[Cr(ox)_3]^{3+}$, all three ligands are the same bidentate ligand, so there is no cis/trans distinction. The complex exists only as the optical pair $\Delta$ and $\Lambda$, giving $2$ stereoisomers.