The number of atoms touching a particular atom in a crystal is called its ……….

Answer

To solve the question, "The number of atoms touching a particular atom in a crystal is called its ……….," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question is asking for a term that describes the number of atoms that are in contact with a specific atom in a crystal structure.

2. **Identifying Key Concepts**: In crystallography, the arrangement of atoms and how they interact with each other is crucial. One important concept is how many neighboring atoms are directly adjacent to a given atom.

3. **Defining the Term**: The term that describes the number of atoms that are in direct contact with a particular atom is known as the "coordination number."

4. **Explaining Coordination Number**: The coordination number is defined as the number of nearest neighbors surrounding a central atom. It indicates how many atoms are touching the atom in question at the minimum distance.

5. **Final Answer**: Therefore, the answer to the question is "coordination number."