The nickel(II) dimethylglyoxime complex, $Ni(dmg)_2$, is a **classic square planar complex** used for the qualitative detection of nickel.
Statement A is correct. The complex is **red in colour**, which is a well-known characteristic of the nickel dimethylglyoxime precipitate.
Statement B is incorrect. The complex is **insoluble in water**, even in alkaline medium. This low solubility is why it precipitates easily at pH ≈ 9.
Statement C is incorrect. Nickel(II) in this complex undergoes **dsp2 hybridisation**, leading to **pairing of electrons**. Hence, the complex is **diamagnetic with zero unpaired electrons**, not two.
Statement D is correct. The complex has a **square planar geometry**, so the **N – Ni – N bond angle is close to 90°**.
Statement E is incorrect. The complex contains **two five-membered chelate rings**, not four. Each dimethylglyoxime ligand forms one five-membered ring with nickel.
Therefore, the incorrect statements are B, C and E.
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