NEET AIPMT SOLVED PAPER SCREENING 2008

  • question_answer
    Percentage of free space in a body centred  cubic unit cell is

    A) 30%    

    B)                        32%                                       

    C) 34%                                       

    D) 28%

    Correct Answer: B

    Solution :

    Key Idea: Packing fraction \[=\frac{\text{Volume occupied by atoms in a unit cell}}{\text{Volume of the unit cell}}\] For body centred cube, Packing fraction \[=\frac{2\times \frac{4}{3}\pi {{r}^{3}}}{{{\left( \frac{4r}{\sqrt{3}} \right)}^{3}}}=\frac{\sqrt{3}\pi }{8}=0.68\]             where, edge length \[a=\frac{4r}{\sqrt{3}}\] \[\therefore \]Volume occupied = 68% and volume vacant = 32%


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