Q20 / 180 · KCET 2021 · Chemistry

In chrysoberyl, a compound containing beryllium, aluminium and oxygen, oxide ions form cubic close packed structure. Aluminium ions occupy $\frac{1}{4}$ th of octahedral voids. The formula of the compound is

  • A
    $\mathrm{BeAlO}_{4}$
  • Correct answer
    B
    $\mathrm{BeAl}_{2} \mathrm{O}_{4}$
  • C
    $\mathrm{Be}_{2} \mathrm{AlO}_{2}$
  • D
    $\mathrm{BeAlO}_{2}$

Solution

Given, chrysoberyl forms ccp structure. Oxygen occupies lattice points $=N$ (say) Al occupies $\frac{1}{2}$ of octahedral voids $=\frac{N}{2}$ Be occupies $\frac{1}{8}$ of tetrahedral voids $=\frac{2 N}{8}$ $\therefore$ The formula of compound is $\begin{aligned} &\mathrm{Be}: \mathrm{Al}: \mathrm{O} \\ &\frac{2 N}{8}: \frac{N}{2}: N \\ &\Rightarrow \quad \mathrm{BeAl}_{2} \mathrm{O}_{4} \end{aligned}$

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

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