InterviewSolution
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InterviewSolution
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Which of the following statements is not correct?A. the number of Bravais lattices in which a crystal can ebh categorized in `44`.B. The fraction of the total volume occupaied by the atoms in a primitive cell is `0.48`.C. Molecular solids are generally volatile.D. The number of `C` atoms in an unit cell of diamond is `4`. |
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Answer» Correct Answer - 2,4 In a simple cubic lattice the edge length (or side of the cube) `a` and the radius of each particle `r` are related as `a=2r` The volume of the cubic unit cell =`a^(3)` `=(2r)^(3)` `=8r^(3)` Since a simple cubic unit cell contains only `1` atom the volume of the occupied space `=4//3pir^(3)` `:.` Packing efficiency `=("volume of one atom")/("Volume of the cubic unit cell")xx100%` ltb rgt `=((4)/(3)pir^(3))/(8r^(3))xx100%` `=(pi)/(6)xx100%` `= 52.4%` Here option `(2)` is not correct . In diamond carbon atom have fcc arrangement with one `C`-atom on each body diagonal (i.e, occupying alternate tetrahedral voids). Structure of diamond is similar to that of zince blende `(ZnS)` Net contribution of `C`-atoms on the corners. `=8xx(1)/(8)=1` Net contribution of `C`-atoms on face centres `=6xx(1)/(2)=3` Net contribution of `C`-atoms on `4` body diagonals `=4xx1=4` therefore total number `C`-atoms per unit cell of diamond is `1+3+4=8`. Hence option `(4)` is also not correct. |
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