If the number of atoms in a unit cell is $2$,then the number of tetrahedral and octahedral voids will be ....... and ....... respectively.

$A$ compound is formed by two elements $X$ and $Y$. Atoms of the element $Y$ (anions) form an $hcp$ structure and atoms of the element $X$ (cations) occupy all the tetrahedral voids. Determine the formula of the compound.

The radius ratio of cation to anion for a triangular void is ....

$A$ compound is formed by elements $P$ and $Q$. Atoms of $Q$ are in $ccp$ arrangement. If $P$ occupies all the tetrahedral voids,what is the formula of the compound?

In a face-centred cubic arrangement of $A$ and $B$ atoms,$A$ atoms are at the corners of the unit cell and $B$ atoms are at the face centres. If one of the $A$ atoms is missing from one corner of the unit cell,what is the simplest formula of the compound?

Which of the following crystal lattice will have a void fraction of $0.476$?