What is the radius ratio $r^+/r^-$ for $NaCl$?

The ratio of the effective number of atoms in a unit cell of $fcc$ and $bcc$ lattices is

Number of atoms per unit cell for body centered cubic system is

The empirical formula for a compound with a cubic close packed arrangement of anions and with cations occupying all the octahedral sites is $A_{x}B$. The value of $x$ is ..... .
(Integer answer)

The unit cell of diamond is composed of:

The number of unit cells present in $39 \ g$ of potassium if it crystallizes as a body-centered cubic $(BCC)$ structure is ($N = \text{Avogadro number}$, $\text{At. wt. of potassium} = 39$).