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 problem of drawing the structures of optical isomers for the given coordination compounds, we will follow a systematic approach for each compound.

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

**Step 1:** Identify the coordination number and geometry.
- Chromium (Cr) in this complex is surrounded by three bidentate oxalate ligands (C2O4), leading to a coordination number of 6. The geometry is octahedral.

**Step 2:** Draw the basic structure.
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