What is the total number of ions present in one unit cell of sodium chloride lattice?

Which of the following expressions is correct for a sodium chloride $(NaCl)$ unit cell with edge length $a$?

If the length of the body diagonal of a $FCC$ unit cell is $x \ \mathring{A}$, the distance between two nearest octahedral voids in the cell in $\mathring{A}$ is

The number of octahedral voids in a $BCC$ structure is:

In a diamond crystal,each carbon atom is linked with other carbon atoms. The number of carbon atoms in a diamond unit cell is:

$A$ certain metal crystallizes in a $bcc$ lattice. The distance between the nearest neighbours is $433 \text{ pm}$. The distance between the next nearest neighbours is :- .............. $\text{pm}$