NEET AIPMT SOLVED PAPER SCREENING 2006

  • question_answer
                    CsBr crystallises in a body centred cubic lattice. The unit cell length is 436.6 pm. Given that the atomic mass of Cs = 133 and that of Br = 80 amu and Avogadro number being \[6.02\times {{10}^{23}}\,mo{{l}^{-1}},\] the density of \[CsBr\] is:

    A)                                                                                                                                                                                            \[42.5\,g/c{{m}^{3}}\]

    B)                 \[0.425\,g/\,c{{m}^{3}}\]

    C)                         \[8.25\,g/\,c{{m}^{3}}\]

    D)                 \[4.25\,g/c{{m}^{3}}\]

    Correct Answer: D

    Solution :

                    Density of \[CsBr\,=\frac{Z\times m}{{{a}^{3}}\times {{N}_{0}}}\]                 \[Z\to \] no. of atoms in the bcc unit cell = 2                 \[M\to \] molar mass of CsBr = 133 + 80 = 2                 \[a\to \] edge length of unit cell                 = 436.6 pm                 \[=436.\,6\times {{10}^{-10}}\,cm\]                 \[\therefore \,\,Density\,=\frac{2\times 213}{{{(436.6\times {{10}^{-10}})}^{3}}\times 6.02\times {{10}^{23}}}\]                 \[=8.50\,g\,/c{{m}^{3}}\]                 For a unit cell = \[\frac{8.50}{2}=4.25\,g/c{{m}^{3}}\]


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