What is the coordination number of $Cs^{+}$ and $Cl^{-}$ ions in the $CsCl$ structure?

$A^{+}B^{-}$ shows rock salt type arrangement. Edge length of unit cell is $6 \ \mathring{A}$. If radius of $A^{+}$ is $1 \ \mathring{A}$,then the incorrect option is:

The coordination number of a metal crystallising in a hexagonal close-packed $(HCP)$ structure is

If the length of the body diagonal of a $FCC$ unit cell is $x \ \mathring{A}$, the distance between two nearest octahedral voids in the cell in $\mathring{A}$ is

$A$ compound $M_pX_q$ has a cubic close packing $(ccp)$ arrangement of $X$. Its unit cell structure is shown below. The empirical formula of the compound is

For some crystals,the radius ratio for cation and anion is $0.525$,its coordination number will be