Which statement about coordination number of a cation is true?

Options

A. Most metal ions exhibit only a single characteristic coordination number
B. The coordination number is equal to the number of ligannds 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

To determine which statement about the coordination number of a cation is true, we can analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Coordination Number**:
- Coordination number refers to the number of ligand atoms that are bonded to a central metal atom in a coordination complex.

2. **Evaluating Each Statement**:
- **Option 1**: "Most metal ions exhibit only a finger characteristic coordination number."
- This statement is **false**. Different metal ions can exhibit various coordination numbers depending on the ligands and their geometries.

- **Option 2**: "Coordination number is equal to the number of ligands bonded to the metal atom."
- This statement is **also false**. The coordination number does not always equal the number of ligands because some ligands can be bidentate or polydentate, meaning they can bond to the metal at multiple points.

- **Option 3**: "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."
- This statement is **incorrect**. While achieving a stable electron configuration is important, the coordination number is influenced by various factors including the size and charge of the cation, as well as the nature of the ligands.

- **Option 4**: "In most of the cations, the coordination number depends upon the size and the charge of the cation."
- This statement is **true**. The coordination number is indeed influenced by the size of the cation and its charge. Larger cations can accommodate more ligands, and higher charged cations can attract more ligands due to increased electrostatic interactions.

3. **Conclusion**:
- The correct statement about the coordination number of a cation is **Option 4**: "In most of the cations, coordination number depends upon the size and the charge of the cation."