Draw the structures of optical isomers of:
(i). `[Cr(C_2O_4)_3]^(3-)`
(ii). `[PtCl_2(en)_2]^(2+)`
(iii). `[Cr(NH_3)_2Cl_2(en)]^(o+)`

Explanation

To solve the question regarding the structures of optical isomers for the given coordination complexes, we will analyze each compound step by step.

### (i) Structure of `[Cr(C_2O_4)_3]^(3-)`

1. **Identify the Coordination Number and Geometry**: Chromium in this complex is coordinated by three bidentate oxalate ligands (C₂O₄²⁻). The coordination number is 6, which typically results in an octahedral geometry.

2. **Draw the Octahedral Structure**: Place the chromium ion at the center and arrange the three bidentate oxalate ligands around it. Each oxalate ligand will occupy two coordination sites.

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