The number of octahedral voids in a unit cell of a cubical closest packed structure is

In the rock salt structure,the number of formula units per unit cell is equal to

In the $NaCl$ crystal structure,how many chloride ions surround each sodium ion?

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

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

Which of the following expressions is correct in the case of a $CsCl$ unit cell (edge length '$a$')?