Which of the following complex is homoleptic?

Identify the homoleptic complex from the given options.

Definition: A homoleptic complex is one in which the central metal ion is bonded to only one type of ligand. A heteroleptic complex has two or more different types of ligands.

Analyzing each option:

Option A: $$[Ni(CN)_4]^{2-}$$ - Ni is bonded to 4 $$CN^-$$ ligands only. One type of ligand. This is homoleptic.

Option B: $$[Ni(NH_3)_2Cl_2]$$ - Ni is bonded to $$NH_3$$ and $$Cl^-$$. Two different ligands. Heteroleptic.

Option C: $$[Fe(NH_3)_4Cl_2]^+$$ - Fe is bonded to $$NH_3$$ and $$Cl^-$$. Two different ligands. Heteroleptic.

Option D: $$[Co(NH_3)_4Cl_2]^+$$ - Co is bonded to $$NH_3$$ and $$Cl^-$$. Two different ligands. Heteroleptic.

The correct answer is Option A: $$[Ni(CN)_4]^{2-}$$.