Question

Which statement about coordination number of a metal ion is true?

• A. Most metal ions exhibit only a single characteristic coordination number.
• B. The coordination number is equal to the number of ligands bonded to the metal atom.
• C. The coordination number is determined solely by the tendency to surround the metal atom with the same number of electrons as one of the rare gases.
• D. For most cations, the coordination number depends on the size, and charge of the cation.

Answer 1

The correct option is D For most cations, the coordination number depends on the size, and charge of the cation.

Some metal ions exhibit more than one coordination number. Hence, the statement A is false.
Coordination number is the number of ligands that are directly attached to the central metal atom or ion in the coordination compound. Here, the ligand is monodentate and attached to the metal via sigma bond. Thus, the statement B is false.
The coordination number is determined by the tendency to surround the metal atom with the same number of electrons as one of the rare gases. In addition, there are several other factors also. Hence, the option C is false.
The coordination number of a metal ion depends on the charge on the metal ion, charge on the ligand, the relative sizes of the metal ion and the ligands and the forces of repulsion between the ligands. Thus, statement D is true.