What are two types of crystal structures shown by ice at different pressures?

In the calcium fluoride structure,the coordination number of the cation and anion are respectively:

$A$ and $B$ atoms in a crystal are positioned at the corners and face centers respectively. What is the formula of the crystal?

For an ionic crystal of the type $AB$,the value of the limiting radius ratio is $0.40$. This value suggests that the crystal structure should be:

$A$ solid has a structure in which $W$ atoms are located at the corners of a cubic lattice, oxygen atoms at the edge centres, and $Na$ atoms at the body centre. The formula of the compound is:

Which statement is correct for $Fe_3O_4$?