Step 1: Understanding the Concept:
Donor atoms are the atoms in ligands that directly donate electron pairs to the central metal ion. Step 2: Key Formula or Approach:
Identify the ligands and their denticity.
$[\text{Ni}(\text{CN})_4]^{2-}$. Step 3: Detailed Explanation:
The name Tetracyanonickelate(II) implies a nickel ion bonded to four cyano ($\text{CN}^-$) groups.
Cyanide ($\text{CN}^-$) is a monodentate ligand, meaning it has one donor atom (typically Carbon in these complexes).
With four such ligands, there are $4 \times 1 = 4$ donor atoms. Step 4: Final Answer:
The total number of donor atoms is 4.