In antifluorite structure,the negative ions

$A$ two-dimensional solid pattern formed by two different atoms $X$ and $Y$ is shown below. The black and white squares represent atoms $X$ and $Y,$ respectively. The simplest formula for the compound based on the unit cell from the pattern is

Which one of the following statements about packing in solids is incorrect?

In a cubic close-packed $(ccp)$ structure,if there are $N$ spheres,what is the number of octahedral voids?

In a crystal lattice,the number of octahedral voids compared to tetrahedral voids is ...............

In a crystal,atoms of $A$ form an $FCC$ lattice,atoms of $B$ occupy all octahedral voids,and atoms of $C$ occupy $25\%$ of the tetrahedral voids. The possible molecular formula of the compound is: