In the fcc arrangement of `A` and `B` atoms whose `A` atoms are at corners of the unit cell and `B` are at the face centres one of the `A` atom is missing from one corner in each unit cell. What is the simplest formula of the compound?

Answer

`A_(7)B_(24)`

Explanation

Contribution made by an atom A present at one corner = 1/8
Contribution made by atoms A at seven corners = 7/8
Contribution made by one face centred atoms A = 1/2
Contribution made by six face centred atoms B = `6xx1//2=3`
`therefore` formula of the compound : `A_((7//8))B or A_(3)B_(24)`.