$A$ crystal is formed by two elements $X$ and $Y$ in a cubic structure. $X$ atoms are at the corners of a cube,while $Y$ atoms are at the face centers. The formula of the compound will be:

In a face centred cubic lattice,atom $A$ occupies the corner positions and atom $B$ occupies the face centre positions. If one atom of $B$ is missing from one of the face centred points,the formula of the compound is:

In an $NaCl$ crystal,how many $Cl^{-}$ ions surround each $Na^{+}$ ion?

The unit cell of a binary compound of $A$ and $B$ metals has a $ccp$ structure with $A$ atoms occupying the corners and $B$ atoms occupying the centres of each face of the cubic unit cell. If during the crystallisation of this alloy,two $A$ atoms are missing from the unit cell,the overall composition per unit cell is:

Coordination number of $Zn^{2+}$ in $ZnS$ (zinc blende) is

In a face-centred cubic $(FCC)$ lattice,atoms of $A$ form the corner points and atoms of $B$ form the face-centred points. If two atoms of $A$ are missing from the corner points,the formula of the ionic compound is