Q86 / 200 · NEET 2008 (Screening) · Chemistry

Which of the following statements is not correct?

  • Correct answer
    A
    The fraction of the total volume occupied by the atoms in a primitive cell is 0.48
  • B
    Molecular solids are generally volatile
  • C
    The number of carbon atoms in an unit cell of diamond is 4
  • D
    The number of Bravais lattices in which a crystal can be categorized is 14

Solution

Key Idea: Packing fraction of lattice structure or fraction of total volume occupied $=\frac{\text { Volume occupied by atoms in a unit cell }}{\text { Volume of the unit cell }}$ Packing fraction of simple cube $\begin{gathered} =\frac{1 \times \frac{4}{3} \pi r^3}{a^3}=\frac{1 \times \frac{4}{3} \pi r^3}{(2 r)^3} \\ =0.52 \end{gathered}$ ($\because$ For primitive cell $a=2 r$) $\therefore$ Volume occupied $=52 \%$

Hence, the correct answer is option: 'A'.

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