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NEET Sample Paper NEET Sample Test Paper-36

  • question_answer
    The pyknometirc density of sodium chloride crystal is \[2.165\times {{10}^{3}}\,kg\,{{m}^{-3}}\]while its X-ray density is \[2.178\times {{10}^{3}}\,kg\,{{m}^{-3}}.\]The fraction of the unoccupied sites in sodium chloride crystal is

    A)  5.96

    B) \[5.96\times {{10}^{-2}}\]

    C) \[5.96\times {{10}^{-1}}\]

    D) \[5.96\times {{10}^{-3}}\] 

    Correct Answer: D

    Solution :

     Molar volume from pyknometric density \[{{V}_{p}}=\frac{M}{2.165\times {{10}^{3}}}{{m}^{3}}\] Molar volume from X-ray density \[{{V}_{x}}=\frac{M}{2.178\times {{10}^{3}}}{{m}^{3}}\] \[\therefore \]Volume unoccupied \[=\frac{M}{{{10}^{3}}}\left( \frac{1}{2.165}-\frac{1}{2.178} \right)\] \[=\frac{0.013\times M\times {{10}^{-3}}}{2.165\times 2.178}{{m}^{3}}\] \[\therefore \] Fraction of volume occupied \[{=\frac{0.013\times M\times {{10}^{3}}}{2.165\times 2.175}}/{\frac{M\times {{10}^{-3}}}{2.165}}\;=5.96\times {{10}^{-3}}\]


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