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JEE Main & Advanced Chemistry The Solid State / ठोस प्रावस्था Question Bank Crystal packing

  • question_answer
    \[Na\] and \[Mg\] crystallize in BCC and FCC type crystals respectively, then the number of atoms of \[Na\] and \[Mg\] present in the unit cell of their respective crystal is [AIEEE 2002]

    A)                 4 and 2

    B)                 9 and 14

    C)                 14 and 9              

    D)                 2 and 4

    Correct Answer: D

    Solution :

           The bcc cell consists of 8 atoms at the corners and one atom at centre.            \ \[n=\left( 8\times \frac{1}{8} \right)+1=2\].            The fcc cell consists of 8 atoms at the eight corners and one atom at each of the six faces. This atom at the face is shared by two unit cells.                                 \ \[n=8\times \frac{1}{8}+\left( 6\times \frac{1}{2} \right)=4\].


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