How many number of atoms present in half of HCP unit cell

Explanation

To determine the number of atoms present in half of a Hexagonal Close-Packed (HCP) unit cell, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the HCP Unit Cell Structure**:
- An HCP unit cell consists of atoms located at the corners, faces, and the center.

2. **Counting Atoms in the HCP Unit Cell**:
- **Corner Atoms**: There are 12 corner atoms in an HCP unit cell. Each corner atom is shared by 6 unit cells, contributing \( \frac{1}{6} \) of an atom per unit cell.
- Total contribution from corner atoms:
\[ 12 \times \frac{1}{6} = 2 \text{ atoms} \]
- **Face Atoms**: There are 2 face atoms in an HCP unit cell. Each face atom is shared by 2 unit cells, contributing \( \frac{1}{2} \) of an atom per unit cell.
- Total contribution from face atoms:
\[ 2 \times \frac{1}{2} = 1 \text{ atom} \]
- **Center Atoms**: There are 3 center atoms in an HCP unit cell, and each contributes fully (1 atom) since they are not shared.
- Total contribution from center atoms:
\[ 3 \times 1 = 3 \text{ atoms} \]

3. **Total Number of Atoms in One HCP Unit Cell**:
- Adding the contributions from all types of atoms:
\[ 2 \text{ (from corners)} + 1 \text{ (from faces)} + 3 \text{ (from centers)} = 6 \text{ atoms} \]

4. **Calculating Atoms in Half of the HCP Unit Cell**:
- Since we need to find the number of atoms in half of the HCP unit cell, we divide the total number of atoms by 2:
\[ \frac{6}{2} = 3 \text{ atoms} \]

### Final Answer:
The number of atoms present in half of the HCP unit cell is **3 atoms**.

---