$($a$)$ From this unit cell, what formula woud you expect for the ionic solid in terms of A$,$ B and $C?$

HINT: Determine the effective number of each ion within the unit cell

$($b$)$ If all the A ions are removed from the unit cell and the ionic radius of $B$ and $C$ are assumed to be represented by $R$ and $Z,$ respectively.

$($i$)$ What will be the coordination number of $C?$

$(2)$

$($ii$)$ What will be the value of the lattice parameter a in terms of $R$ and $Z?$ Show all the steps in deriving the relationship.

$(5)$

$[10]$