Which of the following contains rock salt structure?

$KBr$ crystallizes in a $fcc$ lattice (similar to $NaCl$). The second nearest neighbor of $K^+$ ion and its number are:

What is the crystal structure of $Na_2O$?

In a $ccp$ lattice of $X$ and $Y$,$X$ atoms are present at the corners while $Y$ atoms are at face centers. What would be the formula of the compound if one of the $X$ atoms from a corner is replaced by a $Z$ atom?

In a face-centered cubic lattice,a unit cell is shared equally by how many unit cells?

What is the coordination number of the $Ca^{2+}$ ion in the fluorite structure?