Which of the following complex is homoleptic?

🧠 One Ligand Type = Homoleptic. That's It.

A homoleptic complex contains only one kind of ligand around the metal. Heteroleptic = mixed ligand types. For a four-option MCQ, just scan each formula's coordination sphere and count distinct ligand species.

🗺️ Scan Each Sphere

(1) $[\mathrm{Ni(CN)_4}]^{2-}$ — four $\mathrm{CN^-}$ only. Homoleptic ✓ (2) $[\mathrm{Ni(NH_3)_2Cl_2}]$ — $\mathrm{NH_3}$ and $\mathrm{Cl^-}$. Heteroleptic. (3) $[\mathrm{Fe(NH_3)_4Cl_2}]^+$ — $\mathrm{NH_3}$ and $\mathrm{Cl^-}$. Heteroleptic. (4) $[\mathrm{Co(NH_3)_4Cl_2}]^+$ — $\mathrm{NH_3}$ and $\mathrm{Cl^-}$. Heteroleptic.

Only option (1) has a single ligand species inside the brackets.

⚡ The "Comma Test"

Read the inside of the square brackets aloud. If you hear two different ligand names ("ammine, chloro"), it's heteroleptic. If you hear only one name repeated, homoleptic. Works in under three seconds.

⚠️ Charge Outside Doesn't Count

The counter-ion outside the brackets ($\mathrm{Cl^-}$ in something like $[\mathrm{Co(NH_3)_6}]\mathrm{Cl_3}$) is not a ligand — it's an ionizable spectator. Don't classify $[\mathrm{Co(NH_3)_6}]\mathrm{Cl_3}$ as heteroleptic just because two species appear in the formula. Inside the brackets only.

$\boxed{\text{Answer: (1) } [\mathrm{Ni(CN)_4}]^{2-}}$