Solid State - Result Question 22

####22. A substance AxBy crystallises in a face centred cubic (fcc) lattice in which atoms A occupy each corner of the cube and atoms B occupy the centres of each face of the cube. Identify the correct composition of the substance AxBy

(2002,1M)

(a) AB3

(b) A4B3

(c) A3B

(d) composition cannot be specified

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Answer:

Correct Answer: 22. (a)

Solution:

  1. In cubic system, a corner contribute 18 th part of atom to one unit cell and a face centre contribute 12 part of atom to one unit cell. Therefore,

Number of A per unit cell =18×8=1

Number of B per unit cell =12×6=3

 Formula =AB3



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