Q19 / 160 · AP EAMCET 2018 (23 Apr Shift 2) · Chemistry

A metal oxide crystallises in a hexagonal close-packed array of oxide ions with two out of every three octahedral holes occupied by metal ions. The formula of metal oxide is

  • A
    $M O$
  • B
    $M_3 \mathrm{O}_4$
  • C
    $M_2 \mathrm{O}_5$
  • Correct answer
    D
    $M_2 \mathrm{O}_3$

Solution

Unit cell of hcp structure $=6$ number of oxide ions per unit cell $=6$ number of octahedral voids $=6$. Since, ferric ions occupy only two out of every three octahedral voids, number of octahedral holes occupied by ferric ions $\frac{2}{3} \times 6=4$ stoichiometric ratio of metal and ion $=4: 6=2: 3$. Hence, formula of metal oxide is $M_2 \mathrm{O}_3$.

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

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