JEE Main 2023 — Coordination Compounds Question with Solution

Option A : $${\mathrm{Fe}}_4{\left[\mathrm{Fe}(\mathrm{CN}{)}_6\right]}_3$$ (Prussian Blue)

Prussian blue is a very stable and intensely colored compound, but it is not soluble in water. The individual cyanide ligands and the iron ions are bonded together strongly, which results in a crystalline structure that does not easily dissociate into its components in water.

Option B : $${\left({\mathrm{NH}}_4\right)}_3\left[\mathrm{As}{\left({\mathrm{Mo}}_3{\mathrm{O}}_{10}\right)}_4\right]$$ (Ammonium Arseno Molybdate)

In this compound, the arsenic and molybdenum atoms are coordinated in a complex polyatomic anion. Despite the presence of ammonium ions, which are generally soluble, the overall complex has a low solubility due to the strong interactions between arsenic, molybdenum, and oxygen within the anion.

Option C : $${\mathrm{K}}_3\left[\mathrm{Co}{\left({\mathrm{NO}}_2\right)}_6\right]$$

This is a potassium salt of an anionic complex. Although potassium salts are generally soluble in water, the nitrite ligands attached to the cobalt in the anion form a tightly bonded structure, resulting in very poor solubility in water.

Option D : $$\left[{\mathrm{Fe}}_3(\mathrm{OH}{)}_2(\mathrm{OAc}{)}_6\right]\mathrm{Cl}$$

This complex is composed of iron atoms coordinated with hydroxide and acetate ligands, and a chloride counterion. Hydroxide and acetate ions are both polar and capable of forming hydrogen bonds with water molecules, which is a key factor in solubility. The chloride ion is also soluble in water. The presence of these ions, combined with the likely overall charge of the complex (since it's paired with a counterion), makes it soluble in water.