The unit cell present in ABAB, closest packing of atoms is:

Options

A. Hexagonal
B. tetragonal
C. face centered cubic
D. primitive cubic

Answer

To determine the unit cell present in ABAB closest packing of atoms, we can analyze the different types of packing arrangements. Here’s a step-by-step solution:

### Step 1: Understand the Packing Types
- Closest packing of atoms can occur in different arrangements. The common types are:
- Hexagonal Close Packing (HCP)
- Cubic Close Packing (CCP) or Face-Centered Cubic (FCC)
- Body-Centered Cubic (BCC)
- Primitive Cubic (PC)

### Step 2: Analyze Hexagonal Close Packing (HCP)
- In HCP, the arrangement of atoms follows an ABAB stacking sequence.
- This means that the first layer (A) is followed by a second layer (B), and then the third layer (A) again, continuing the pattern.

### Step 3: Analyze Tetragonal Packing
- Tetragonal packing can be either primitive or body-centered.
- In the primitive tetragonal unit cell, the arrangement is AA, and in the body-centered tetragonal, it can be ABAB.
- However, the body-centered tetragonal is not the same as the ABAB closest packing seen in HCP.

### Step 4: Analyze Face-Centered Cubic (FCC)
- In FCC, the arrangement follows an ABCABC stacking sequence, which is different from ABAB.
- Therefore, FCC does not exhibit the ABAB closest packing.

### Step 5: Analyze Primitive Cubic Packing
- In primitive cubic packing, the arrangement is AA, which does not correspond to ABAB.

### Conclusion
- The only arrangement that exhibits the ABAB closest packing is the **Hexagonal Close Packing (HCP)**.

### Final Answer
The unit cell present in ABAB closest packing of atoms is **Hexagonal Close Packing (HCP)**.

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