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KVPY Sample Paper KVPY Stream-SX Model Paper-14

  • question_answer
    The wurtzite structure is described as hcp of \[{{S}^{2\,-}}\]ions with the alternate tetrahedral voids occupied by \[Z{{n}^{2+}}\]ions. A compound containing A, Band X atoms had the A and B atoms arranged as \[Z{{n}^{2+}}\]and \[{{S}^{2\,-}}\]respectively in the hcp lattice. The X atoms occupied alternate octahedral voids. Which of the following is incorrect?

    A) Formula of the compound is \[{{A}_{2}}{{B}_{2}}X\]

    B) Coordination number of A can be 4.

    C) Coordination number of X can be 6.

    D) Centres of 12 A atoms lie on the edges of one unit cell.

    Correct Answer: D

    Solution :

    B like \[{{S}^{2-}}\] (making hcp)
    A like \[Z{{n}^{2+}}\] (alternate tetrahedral void)
    X (alternate octahedral void)
    no. of B in one unit cell = 6
    no. of A in one unit cell \[=\frac{1}{2}\times 12=6\]
    no. of X in one unit cell \[=\frac{1}{2}\times 6=3\]
    \[\Rightarrow \] Formula   \[{{A}_{6}}{{B}_{6}}{{X}_{3}}\]\[\Rightarrow \]\[{{A}_{2}}{{B}_{2}}X\]
    \[\because \] A is in tetrahedral void, so, coordination number is 4.
    \[\because \] X is in octahedral void, so, coordination number is 6.
    when alternate tetrahedral voids are occupied, then centres of 6 A atoms lies on the edges of one unit cell.


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