Answer: [Ni(CN) 4 ] 2-.
- A [CoF<sub>6</sub>]<sup>3-</sup>
- B [Fe(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup>
- C [NiCl<sub>4</sub>]<sup>2-</sup>
- D [Ni(CN)<sub>4</sub>]<sup>2-</sup>
Correct answer: D. [Ni(CN)<sub>4</sub>]<sup>2-</sup>
Explanation: [Ni(CN)<sub>4</sub>]<sup>2-</sup> is square planar (dsp<sup>2</sup>) with Ni(II) d<sup>8</sup> fully paired, so it is diamagnetic; the other three have unpaired electrons.
The three common coordination geometries: octahedral (6 ligands), tetrahedral (4 ligands), and square planar (4 ligands in one plane).
Concept context
Study of compounds where a central metal atom is bonded to surrounding ligands. Covers nomenclature, types of isomerism, bonding theories (VBT, CFT), and applications in medicine, photography, and industry.