The packing efficiency and coordination number of face-centred cubic $(FCC)$ lattice is

The vacant space in the $bcc$ unit cell is .............. $\%$

$A$ unit cell of calcium fluoride has four calcium ions. The number of fluoride ions in the unit cell is

Find the radius of an atom in $fcc$ unit cell having edge length $393 \ pm$. (in $pm$)

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?

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)