What do you mean by the term coordination number? What is the coordination of each sphere in hcp strucutre

Explanation

### Step-by-Step Solution:

1. **Definition of Coordination Number**:
- The coordination number is defined as the number of nearest neighboring spheres (or atoms) that are in direct contact with a given sphere (or atom) in a crystal structure.

2. **Understanding HCP Structure**:
- The hexagonal close-packed (hcp) structure is a type of crystal lattice arrangement where spheres are packed closely together in a hexagonal formation.

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