Solid State - Result Question 8

####8. A compound of formula A2B3 has the hep lattice. Which atom forms the hcp lattice and what fraction of tetrahedral voids is occupied by the other atoms ? (2019 Main, 10 Jan II)

(a) hcp lattice- A,23 tetrahedral voids- B

(b) hcp lattice- A,13 tetrahedral voids- B

(c) hcp lattice- B,13 tetrahedral voids- A

(d) hcp lattice- B,23 tetrahedral voids- A

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Answer:

Correct Answer: 8. (c)

Solution:

  1. Total effective number of atoms in hcp unit lattice = Number of octahedral voids in hcp=6

Number of tetrahedral voids (TV) in hcp

=2× Number of atoms in hep lattice  =2×6=12

As, formula of the lattice is A2B3.

Suppose, A B
(13×TV) (hcp)
13×12 6
23 1
2 3

So, A=13 tetrahedral voids, B= hcp lattice



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