Question

In a face centred cubic lattice, atom A occupies the corner positions and atom B occupies the face centre positions . If one atom of B is missing from one of the face centred points, the formula of the compound is :
A. `AB_2`
B. `A_2B_3`
C. `A_2B_5`
D. `A_2B`

Answer 1

Correct Answer - C
Contribution by atoms A on the corners 4=`8xx1/8=1`
Contribution by atoms B on the face centres =`5xx1/5=5/2`
(Total atoms on face centres=6. As one atom is missing, atoms actually present=5)
`therefore` Ratio of A:B=`1:5/2=2:5`
Hence, formula =`A_2B_5`