How many formula units are present in the unit cell of fluorite $(CaF_2)$?

How many formula units are there in the unit cell of sodium chloride $(NaCl)$?

In a face-centered cubic lattice of $X$ and $Y$ atoms,$X$ atoms are present at the corners while $Y$ atoms are at the face centers. If two atoms of $X$ are missing from the corners,what is the formula of the compound?

$A^{+}B^{-}$ shows rock salt type arrangement. Edge length of unit cell is $6 \ \mathring{A}$. If radius of $A^{+}$ is $1 \ \mathring{A}$,then the incorrect option is:

An element has a face-centred cubic $(fcc)$ structure with a cell edge of $a$. The distance between the centres of two nearest tetrahedral voids in the lattice is

What is the mass of a $bcc$ type unit cell of sodium if the mass of one atom of sodium is $3.819 \times 10^{-23} \ g$?