Designation of the pattern as AB, AB, AB...... etc., of successive vertical layers of identical atoms gives the arrangement called as :

Options

A. Hexagonal close packing (hcp)
B. Cubic close packing (ccp)
C. Face centered cubic (fcc)
D. Body centered cubic (bcc)

Answer

To solve the question regarding the designation of the pattern as AB, AB, AB... etc., of successive vertical layers of identical atoms, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Pattern**: The pattern given is AB, AB, AB..., which indicates a repeating sequence of two layers. This means that for every A layer, there is a corresponding B layer directly above it.

2. **Identify the Arrangement**: In crystal structures, different arrangements of atoms can be described based on how these layers stack. The AB, AB pattern suggests a specific type of close packing.

3. **Recall Types of Close Packing**:
- **Hexagonal Close Packing (HCP)**: This arrangement consists of alternating layers of atoms, where the first layer is A, the second layer is B, and the third layer returns to A, continuing this pattern.
- **Cubic Close Packing (CCP)** or **Face-Centered Cubic (FCC)**: This arrangement has a repeating pattern of three layers (A, B, C).
- **Body-Centered Cubic (BCC)**: This arrangement has a different structure where there is one atom at each corner of the cube and one atom in the center.

4. **Match the Pattern**: Since the question specifies an AB, AB pattern, it aligns with the structure of Hexagonal Close Packing (HCP), where the layers alternate between A and B without introducing a third layer.

5. **Conclusion**: Therefore, the arrangement corresponding to the AB, AB pattern is Hexagonal Close Packing.

### Final Answer:
The arrangement called as Hexagonal Close Packing (HCP).