KEAM 2015 Physics and Chemistry Paper

Let number of octahedral holes in the lattice =x
∴ Number of tetrahedral holes in the lattice =2x
( ∵ Number of tetrahedral holes =2× number of octahedral holes)
Now, A+ ions occupy 25% of tetrahedral holes. Hence, number of tetrahedral holes occupied in the lattice =2x×25%=2x×‌

25

100

=‌

x

2

since, number of octahedral holes = Number of lattice points.
∴ Number of octahedral holes =x
∴ Molecular formula of the crystal is
Ax/2Bx or AB2