Which of the following metals has different geometry compared to those of the others ?

Options

A. Fe
B. Co
C. Ni
D. Cu

Explanation

To determine which metal has a different geometry compared to the others, we will analyze the packing arrangements of the given metals: iron, cobalt, nickel, and copper.

### Step-by-Step Solution:

1. **Identify the Metals and Their Arrangements:**
- **Iron (Fe)**: Iron exists in a hexagonal close-packed (HCP) arrangement.
- **Cobalt (Co)**: Cobalt exists in a cubic close-packed (CCP) arrangement.
- **Nickel (Ni)**: Nickel also exists in a cubic close-packed (CCP) arrangement.
- **Copper (Cu)**: Copper exists in a cubic close-packed (CCP) arrangement.

2. **Understand the Packing Arrangements:**
- **Hexagonal Close Packing (HCP)**: In HCP, the arrangement of atoms is such that they form a hexagonal structure, and the number of atoms per unit cell (Z) is 6.
- **Cubic Close Packing (CCP)**: In CCP, the arrangement of atoms forms a cubic structure, and the number of atoms per unit cell (Z) is 4.

3. **Count the Void Types:**
- In HCP:
- Octahedral voids = 6 (equal to the number of atoms per unit cell)
- Tetrahedral voids = 12
- In CCP:
- Octahedral voids = 4 (equal to the number of atoms per unit cell)
- Tetrahedral voids = 8 (twice the number of atoms per unit cell)

4. **Compare the Geometries:**
- From the above analysis, we see that iron has a different packing arrangement (HCP) compared to cobalt, nickel, and copper, which all share the same packing arrangement (CCP).

5. **Conclusion:**
- Therefore, the metal that has a different geometry compared to the others is **Iron (Fe)**.

### Final Answer:
The correct answer is **Iron (Fe)**.