Radii of A+ and that of X- and Y- have been given as A+=1.00pmX-=1.00pmY-=2.00pmThus, ratio of volume of AX and AY unit cells is

Ratio of r+/r-  will decide the type of unit cell. For AX,  rA+rX-=11=1.0, hence, AX has bcc structure.∴2(rA+rX-)=a3a=23(rA++rX-)=2×23=43pmVolume (AX)=a3=(43)3=6433ForAYrA+rY-=12=0.5Thus, for octahedral or square planar structure r=a2∴a=2r=2(rA++rY-)=2(1+2)=6pmVolume (AY)=a3=216pm3∴Ratio=Volume(AX)Volume (AY)=6433×216=0.057