Which of the following complex is homoleptic?

Homoleptic complexes are compounds in which all the ligands bound to the central metal atom or ion are identical.

Homoleptic complexes have only one type of ligand.

${\left[\mathrm{Ni}(\mathrm{CN}{)}_4\right]}^{2-}$ has only one type of ligand.

Hence, option A is the answer.