Three-dimensional close packing in solids is referred to as stacking the second square closed packing exactly above the first. In this tight packing, the spheres are horizontally and vertically correctly balanced. Similarly, we can obtain a simple cubic lattice by adding more layers, one above the other. This can be done in two ways. Three-dimensional close packing from two-dimensional square close-packed layers: By putting the second square closed packing exactly above the first, it is possible to form three-dimensional close packing. In this tight packing, the spheres are horizontally and vertically correctly balanced. Similarly, we can obtain a simple cubic lattice by adding more layers, one above the other.Three-dimensional close packing from two-dimensional hexagonal close-packed layers: With the assistance, of two-dimensional hexagonal packed layers, three-dimensional close packing can be obtained.
The coordination number of cubic closed packing is:

Options

A. 6
B. 8
C. 12
D. 4

Explanation

To determine the coordination number of cubic close packing (CCP), we can follow these steps:

### Step 1: Understanding the Structure of CCP
Cubic close packing, also known as face-centered cubic (FCC), is a type of three-dimensional close packing of spheres. In this arrangement, spheres are located at each of the corners of the cube and at the centers of each of the cube's faces.

**Hint:** Visualize the arrangement of spheres in a cube to understand how they are positioned.

### Step 2: Counting the Spheres in the Unit Cell
In a face-centered cubic structure, there are:
- 8 corner spheres, each shared by 8 adjacent unit cells (1/8 contribution per unit cell).
- 6 face-centered spheres, each shared by 2 adjacent unit cells (1/2 contribution per unit cell).

**Calculation:**
- Contribution from corner spheres: \(8 \times \frac{1}{8} = 1\)
- Contribution from face-centered spheres: \(6 \times \frac{1}{2} = 3\)

Total number of spheres in one unit cell = \(1 + 3 = 4\).

**Hint:** Remember that the contribution of spheres depends on how many unit cells share them.

### Step 3: Identifying Neighbors
The coordination number is defined as the number of nearest neighbor spheres surrounding a given sphere. In the FCC structure:
- Each sphere at the center of the cube is surrounded by 12 other spheres.

**Hint:** Visualize the arrangement and count the nearest neighbors around a single sphere.

### Step 4: Conclusion
Thus, the coordination number of cubic close packing (CCP) or face-centered cubic (FCC) is **12**.

**Final Answer:** The coordination number of cubic closed packing is **12**.