What is the coordination number in a hexagonal close-packed $(h.c.p.)$ structure?

$A$ cubic structure is formed where atoms of element $X$ are occupied at the corners of the cube and also at the face centers. Atoms of element $Y$ are present at the body center and at the edge centers. If all the atoms are removed along a plane passing through the middle of the cube (bisecting the four edges), the formula will become

In a $ccp$ lattice of $X$ and $Y$,$X$ atoms are present at the corners while $Y$ atoms are at face centers. What would be the formula of the compound if one of the $X$ atoms from a corner is replaced by a $Z$ atom?

Number of next nearest ions around $Na^{+}$ in $NaCl$ unit cell is $X$ and number of next nearest ions around $Cs^{+}$ in $CsCl$ unit cell is $Y$. The value of $X - Y$ is

Calculate the total number of atoms in a $bcc$ crystal lattice containing $2 \times 10^{23}$ unit cells.

$A$ compound having elements $X$ and $Y$ crystallises in a cubic structure, where $X$ is at the corner position and $Y$ is at the center of the cube. The correct formula of the compound is