The percentage of unoccupied volume in a simple cubic cell is (in $\%$)

In a solid $AB_2$,the coordination number of $A$ is $8$. It has a cubic close-packed $(ccp)$ lattice. Half of the $B$ atoms are,however,ejected from the solid. Now,the number of tetrahedral holes (voids) that remain filled is:

$A$ solid is made of two elements $X$ and $Y$. Atoms of $X$ are in $FCC$ arrangement and $Y$ atoms occupy all tetrahedral sites. What is the possible formula of the compound?

$A$ compound is formed by two elements $A$ and $B$. The element $B$ forms a cubic close-packed $(CCP)$ structure and atoms of $A$ occupy $\frac{1}{3}$ of the tetrahedral voids. If the formula of the compound is $A_x B_y$,then the value of $x+y$ is:

In a $ccp$ structure of $X$ atoms,$Y$ atoms occupy the octahedral voids. If two $X$ atoms at the corners are replaced by $Z$ atoms,the molecular formula of the solid will be:

In a mixed oxide of $A$ and $B$,$A$ occupies all the octahedral voids while $B$ occupies $(2/3)$rd of the tetrahedral voids. The molecular formula of this oxide is