What is the coordination number of a cation in an ionic compound if the type of hole occupied by the cation is cubic?

An oxide of $A$ crystallizes with $8$ atoms at the corners of the unit cell and $18$ oxygen atoms on the edges and on the faces symmetrically. What is the formula of this oxide?

The vacant space in the $bcc$ unit cell is .............. $\%$

What is the number of atoms present in the unit cells of a simple cubic,body-centered cubic,and face-centered cubic lattice of a monoatomic substance,respectively?

The ionic radii of $A^{+}$ and $B^{-}$ ions are $0.98 \times 10^{-10} \ m$ and $1.81 \times 10^{-10} \ m$. The coordination number of each ion in $AB$ is.......

$A$ 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