The arrangement of the first two layers, one above the other, in hep and ccp arrangement is

Options

A. Exactly same in both cases
B. Partly same and partly different
C. Different from each other
D. Nothing definite

Answer

To determine the arrangement of the first two layers in Hexagonal Close Packing (HCP) and Cubic Close Packing (CCP), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definitions**:
- **HCP (Hexagonal Close Packing)**: In this arrangement, the spheres are packed in a hexagonal pattern. Each sphere in one layer is surrounded by six spheres in the same layer.
- **CCP (Cubic Close Packing)**: In this arrangement, the spheres are packed in a cubic pattern. Each sphere in one layer is surrounded by four spheres in the same layer.

2. **Visualize the First Layer**:
- For both HCP and CCP, the first layer consists of spheres arranged in a close-packed manner. In HCP, this is a hexagonal arrangement, while in CCP, it is a square arrangement when viewed from above.

3. **Visualize the Second Layer**:
- In HCP, the second layer is placed directly above the first layer, with the spheres fitting into the depressions of the first layer. This arrangement continues to maintain the hexagonal pattern.
- In CCP, the second layer is also placed directly above the first layer, but the spheres fit into the tetrahedral and octahedral voids created by the first layer, maintaining the cubic symmetry.

4. **Comparison of the First Two Layers**:
- Despite the different geometric arrangements (hexagonal for HCP and cubic for CCP), the first two layers in both arrangements are similar in that they both consist of close-packed spheres. The arrangement of the first layer in both cases is the same, and the second layer is positioned in a way that maintains the close packing.

5. **Conclusion**:
- The arrangement of the first two layers in HCP and CCP is the same in terms of close packing, but the geometric arrangement differs. Therefore, while the layers are arranged similarly in terms of packing efficiency, they differ in geometry.

### Final Answer:
The arrangement of the first two layers, one above the other, in HCP and CCP is the same in terms of packing efficiency, but they differ geometrically.

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