Question

In a face centred cubic lattice, atom A occupies the corner positions and atom B occupies the face centre positions. If one atoms of B is missing from one of the face centred points, the formula of the compound is :
A. `AB_(2)`
B. `A_(2)B_(3)`
C. `A_(5)B_(5)`
D. `A_(2)B`

Answer 1

Correct Answer - B
Contribution by atoms A on the corners
` 4= 8 xx 1/8 =1 `
Contribution by atoms B on the face centres
` 5 xx 1/2 = 5/2 `
( Total atoms on face centres = 6. As one atoms is missing , atoms actually present = 5)
: Ration of A: B = ` 1 : 5/2 = 2: 5`
Henece, formula ` = A_(2)B_(5)`