Question

The unit cell of a binary compound of A and B has ccp structure with A atoms occupying the corners and B atoms occupying the centres of each face of the unit cell. If during crystallisation of the alloy, in the unit cell two atoms of A are missing, the overall composition per unit cell is :
A. `AB_6`
B. `AB_4`
C. `AB_8`
D. `A_6B_24`

Answer 1

Correct Answer - D
Permitted coordination number for ccp is 8 , but 2A atoms are missing
`therefore " Contribution of A `=6xx1/8=6/8`
Contribution of B `=6xx1/2=3, " So" , A_(6//8)B_3 " or " A_6B_(24)`