What is the coordination number in a square close packed structures in two dimensions?

Options

A. 2
B. 3
C. 4
D. 6

Explanation

To determine the coordination number in a square close-packed (SCP) structure in two dimensions, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Structure**:
- In a square close-packed structure, atoms are arranged in a two-dimensional square grid. Each atom is positioned at the corners of squares formed by neighboring atoms.

2. **Identifying the Atoms**:
- Let's denote the atoms in the structure as 'A'. In this arrangement, each atom is surrounded by other atoms.

3. **Finding Neighboring Atoms**:
- For a single atom (let's say the central atom), we need to identify how many neighboring atoms are in direct contact with it. In a square arrangement, each atom will have neighbors to the left, right, above, and below.

4. **Counting the Neighbors**:
- The atom has:
- 1 neighbor directly to the left,
- 1 neighbor directly to the right,
- 1 neighbor directly above,
- 1 neighbor directly below.
- Therefore, the total number of neighboring atoms surrounding the central atom is 4.

5. **Conclusion**:
- The coordination number, which is defined as the number of nearest neighboring atoms surrounding a central atom, in a square close-packed structure in two dimensions is thus 4.

### Final Answer:
The coordination number in a square close-packed structure in two dimensions is **4**.