Which from following complexes contains only anionic ligands?

Which from following complexes contains only anionic ligands?
  1. Tetraamminedibromoplatinum (IV) bromide
  2. Potassium trioxalatoaluminate (III)
  3. Pentaaquaisothiocyanatoiron (III) ion
  4. Pentaammineaquacobalt (III) iodide

Solution

Potassium trioxalatoaluminate (III): $\mathrm{K}_3\left[\mathrm{Al}\left(\mathrm{C}_2 \mathrm{O}_4\right)_3\right]$ Oxalate ion $\left(\mathrm{C}_2 \mathrm{O}_4^{2-}\right)$ is an anionic ligand.

Asked in: MHT CET 2023 (12 May Shift 1)

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