The CORRECT statement(s) for cubic close packed (ccp) three dimensional structure is (are)

In the middle layer, an atom present at the center has 6 neighboring atoms, 3 neighboring atoms in the top layer and 3 neighboring atoms in the bottom layer. Total 12 neighboring atoms. The top-most layer will have 9 nearest neighbors.

$\begin{array}{l}\mathrm{Packing} \mathrm{efficiency}=\frac{\mathrm{volume} \mathrm{occupies} \mathrm{by} 4 \mathrm{spheres} \mathrm{in} \mathrm{unit} \mathrm{cell}}{\text{ total volume of unit cell }}\times 100\\ =\frac{4\times {\displaystyle \frac{4}{3}}{\mathrm{\pi r}}^3}{{\mathrm{a}}^3}\times 100\\ =\frac{4\times {\displaystyle \frac{4}{3}}{\mathrm{\pi r}}^3}{(2\sqrt{2}\mathrm{r}{)}^3}\times 100\\ =74\mathrm{\%}\end{array}$

In CCP,  number of octahedral voids = 1 × no. of atom
Number of tetrahedral voids = 2 × no. of atom 
Hence, the number of octahedral and tetrahedral voids per atom are 1 and 2, respectively.
For edge length:

$$\begin{gathered} 4\mathrm{r}=\sqrt{2}\mathrm{a} \\ \mathrm{a}=2\sqrt{2}\mathrm{r} \end{gathered}$$

Where ‘a’ is edge length of unit cell and ‘r’ is radius of atom.