Which of the following describes the hexagonal close packed arrangement of spheres ?

Options

A. ABCABA
B. ABCABC
C. ABABAB
D. ABBABB

Answer

To describe the hexagonal close packed (HCP) arrangement of spheres, we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding the Basic Structure**:
- The hexagonal close packed arrangement consists of layers of spheres (atoms) stacked in a specific pattern.

2. **Layer Arrangement**:
- The first layer can be visualized as a flat arrangement of spheres. Let's denote this layer as Layer A.
- The second layer is placed above the first layer, and it fits into the gaps of the first layer. This layer is denoted as Layer B.

3. **Repeating Layers**:
- The third layer is identical to the first layer (Layer A), and the fourth layer is identical to the second layer (Layer B).
- This creates a repeating pattern of layers: ABABAB...

4. **Hexagonal Shape**:
- In this arrangement, each sphere in Layer A is surrounded by six spheres from Layer B, forming a hexagonal shape. This is a key characteristic of the HCP structure.

5. **Coordination Number**:
- In a hexagonal close packed structure, each sphere has a coordination number of 12, meaning each sphere is in contact with 12 other spheres.

6. **Conclusion**:
- The hexagonal close packed arrangement can be described as an ABAB type of arrangement, where the first and third layers are the same (A), and the second and fourth layers are the same (B).

### Final Answer:
The hexagonal close packed arrangement of spheres is characterized by an ABAB type of stacking, where the first and third layers are identical, and the second and fourth layers are identical, forming a hexagonal shape around each sphere.

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