The correct statement about, CCP structure is

Options

A. Packing fraction = 26%
B. Coordination number = 6
C. Unit cell is face centred cubic
D. AB - AB type of packing

Answer

To determine the correct statement about the CCP (Cubic Close Packing) structure, let's analyze the information step-by-step.

### Step-by-Step Solution:

1. **Understanding Packing Fraction**:
- The packing fraction is defined as the ratio of the volume occupied by the spheres (atoms) in the unit cell to the total volume of the unit cell.
- For CCP, the formula for packing fraction is:
\[ \text{Packing Fraction} = \left( \frac{\text{Volume occupied by spheres}}{\text{Total volume of unit cell}} \right) \times 100 \]

2. **Volume of Spheres in CCP**:
- In a CCP structure, there are 4 effective atoms per unit cell.
- The volume of one sphere (atom) is given by:
\[ V_{\text{sphere}} = \frac{4}{3} \pi r^3 \]
- Therefore, the total volume occupied by 4 spheres is:
\[ V_{\text{occupied}} = 4 \times \frac{4}{3} \pi r^3 = \frac{16}{3} \pi r^3 \]

3. **Volume of the Unit Cell**:
- The unit cell in CCP is a cube with edge length \( a \).
- The volume of the cube is:
\[ V_{\text{cell}} = a^3 \]

4. **Relationship between Edge Length and Radius**:
- The relationship between the edge length \( a \) and the radius \( r \) in CCP is:
\[ a = 2\sqrt{2}r \]
- Thus, the volume of the unit cell can be expressed as:
\[ V_{\text{cell}} = (2\sqrt{2}r)^3 = 16\sqrt{2}r^3 \]

5. **Calculating the Packing Fraction**:
- Now substituting the volumes into the packing fraction formula:
\[ \text{Packing Fraction} = \left( \frac{\frac{16}{3} \pi r^3}{16\sqrt{2}r^3} \right) \times 100 \]
- Simplifying this gives:
\[ \text{Packing Fraction} = \left( \frac{16\pi}{48\sqrt{2}} \right) \times 100 = \frac{\pi}{3\sqrt{2}} \times 100 \]
- Approximating this value results in approximately 74%.

6. **Coordination Number**:
- The coordination number in a CCP structure is the number of nearest neighbor atoms surrounding a central atom.
- In CCP, the coordination number is 12, as each atom is in contact with 12 others.

7. **Unit Cell Type**:
- The CCP structure is also known as a face-centered cubic (FCC) structure.

8. **Packing Type**:
- The packing in CCP is ABCABC type, not ABAB type.

### Conclusion:
From the analysis, we can conclude that:
- The correct statement about CCP structure is that it is a face-centered cubic structure with a packing fraction of approximately 74% and a coordination number of 12.