The number of ligands attached to the central atom is termed the ___________of the central atom .

Answer

**Step-by-Step Solution:**

1. **Understanding the Concept of Ligands:**
- Ligands are ions or molecules that can donate a pair of electrons to a central atom in a coordination complex. They are essential in forming coordination compounds.

2. **Identifying the Central Atom:**
- In a coordination compound, the central atom is usually a metal ion that is surrounded by ligands.

3. **Definition of Coordination Number:**
- The coordination number is defined as the number of ligands that are attached to the central atom in a coordination complex.

4. **Examples to Illustrate Coordination Number:**
- For instance, in the complex nickel tetra carbonyl (Ni(CO)₄), nickel is the central atom, and it is surrounded by four carbon monoxide (CO) ligands. Thus, the coordination number of nickel is 4.
- Another example is platinum (NH₃)₂Cl₂. Here, platinum is the central atom, with two ammonia (NH₃) ligands and two chloride (Cl) ligands attached. The total coordination number is 4 (2 from NH₃ and 2 from Cl).

5. **Conclusion:**
- Therefore, the number of ligands attached to the central atom is termed the **coordination number** of the central atom.

**Final Answer:**
The number of ligands attached to the central atom is termed the **coordination number** of the central atom.

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