Question

The co-ordination number of Cu in [Cu(CN)$_4$]$^{3-$ ion is:}

• A. 2
• B. 3
• C. 4
• D. None of them

Hint:

The coordination number depends on the number of ligand donor atoms bonded, not on the charge of the ion. For example, [Cu(NH$_3$)$_4$]$^{2+}$ and [Cu(CN)$_4$]$^{3-}$ both have a coordination number of 4.

Answer 1

The Correct Option is C

Step 1: Recall definition of coordination number.
The coordination number of a central metal atom in a complex is the number of ligand donor atoms directly bonded to it.

Step 2: Identify ligands in [Cu(CN)$_4$]$^{3-$.}
- The ligand present is CN$^-$.
- Each CN$^-$ ligand donates one pair of electrons through its carbon atom.

Step 3: Count the number of ligands.
There are 4 cyanide ligands attached to Cu. Therefore, the number of Cu–C bonds formed = 4.

Step 4: Conclusion.
Hence, the coordination number of Cu in [Cu(CN)$_4$]$^{3-}$ is 4.
\[ \boxed{4} \]