1. Identify the structure

Cubic close packing (ccp) is the same as face-centered cubic (fcc) packing.

For ccp/fcc:

• Coordination number of a bulk atom $=12$
• Packing efficiency $=74\%$
• Number of octahedral voids per atom $=1$
• Number of tetrahedral voids per atom $=2$
• Edge length relation: $a = 2\sqrt{2}\,r$

2. Check each option

Option A:

"The number of the nearest neighbours of an atom present in the topmost layer is 12"

This statement is not correct as written.

In a ccp structure, an atom in the bulk has coordination number $12$. But an atom in the topmost layer is on the surface, so it does not have all 12 nearest neighbours because atoms are missing above it.

Hence, A is incorrect.

Option B:

"The efficiency of an atom packing is 74%"

For ccp/fcc packing, $\text{Packing efficiency} = 74\%$

Hence, B is correct.

Option C:

"The number of octahedral and tetrahedral voids per atom are 1 and 2, respectively"

In ccp/fcc packing:

• octahedral voids per atom $=1$
• tetrahedral voids per atom $=2$

Hence, C is correct.

Option D:

"The unit cell edge length is } 2\sqrt 2 \text{ times the radius of the atom"

For fcc, atoms touch along the face diagonal.

Face diagonal $= a\sqrt{2}$

Along one face diagonal, there are four radii: $a\sqrt{2} = 4r$ $a = \frac{4r}{\sqrt{2}} = 2\sqrt{2}\,r$

Hence, D is correct.

3. Final derived answer

Correct statements are: $\boxed{B,\ C,\ D}$

4. Comparison with stored correct answer

Stored correct answer: C, B, D

This matches my derived answer exactly (order does not matter).