What is the coordination number of $Cu$ in a face-centered cubic $(fcc)$ lattice?

The structure of $MgO$ is similar to $NaCl$. What would be the coordination number of magnesium?

$A$ crystal is made up of metal ions $M_1$ and $M_2$ and oxide ions. Oxide ions form a $ccp$ lattice structure. The cation $M_1$ occupies $50 \%$ of octahedral voids and the cation $M_2$ occupies $12.5 \%$ of tetrahedral voids of the oxide lattice. The oxidation numbers of $M_1$ and $M_2$ are,respectively:

The edge lengths of a simple cubic $(sc)$ and a face-centered cubic $(fcc)$ unit cell are equal. The ratio of the volume occupied by atoms in these two structures is .....

The solid $AB$ has a $NaCl$ type structure. If the radius of the $A^{+}$ ion is $120 \, pm$, then the maximum radius of the $B^{-}$ ion will be ........... $pm$.

In a compound formed by $A^{+}$ and $B^{-}$ ions,$B^{-}$ ions are arranged at all corners except two and at all face centers except three,while $A^{+}$ ions are at the midpoints of all body diagonals. The molecular formula of the compound will be ................