How does the structure of $NaCl$ transform into the $CsCl$ structure?

Which of the following is correct for the crystal lattices mentioned below?

By increasing the pressure on $NaCl$ crystal,its coordination number will

$A$ cubic structure is formed where atoms of element $X$ are occupied at the corners of the cube and also at the face centers. Atoms of element $Y$ are present at the body center and at the edge centers. If all the atoms are removed along a plane passing through the middle of the cube (bisecting the four edges), the formula will become

In a $BCC$ lattice containing $X$ and $Y$ type of atoms, $X$ type of atoms are present at the corners and $Y$ type of atoms are present at the body center. In its unit cell, if three atoms are missing from the corners, the formula of the compound is:

If the radius ratio for an ionic solid is $0.5248$ and the radius of the cation is $0.95 \ \mathring{A}$,what is the radius of the anion?