In a cubic crystal anions are arranged in fcc arrangement and the cations occupy all the octahedral voids and half the tetrahederal voids. The ratio of the cations and anions in the crystal is

Options

A. `1:1`
B. `2:1`
C. `1:2`
D. `3:2`

Answer

B

Explanation

For fcc arrangement
No. of anion = 4
Fro each atom, there is one octahedral site and 2 tetrahedral sites. Therefore, for 4 anions, there will be 4 octahedral sites and 8 tetrahedral sites.
No. of cations `= 4 xx 1 + 8 xx ( 1)/( 2) = 8`
Ratio of cation and anion `= 8 : 4 ` or `2:1`