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Question: Answered & Verified by Expert
A mineral consists of a cubic close-packed structure formed by $\mathrm{O}^{2-}$ ions where half the octahedral voids are occupied by $\mathrm{Al}^{3+}$ and oneeighth of the tetrahedral voids are occupied by $\mathrm{Mn}^{2+}$. The chemical formula of the mineral is
ChemistrySolid StateKVPYKVPY 2017 (5 Nov SB/SX)
Options:
  • A $\mathrm{Mn}_{3} \mathrm{Al}_{2} \mathrm{O}_{6}$
  • B $\mathrm{MnAl}_{2} \mathrm{O}_{4}$
  • C $\mathrm{MnAl}_{4} \mathrm{O}_{7}$
  • D $\mathrm{Mn}_{2} \mathrm{Al}_{2} \mathrm{O}_{5}$
Solution:
2586 Upvotes Verified Answer
The correct answer is: $\mathrm{MnAl}_{2} \mathrm{O}_{4}$
No of $\mathrm{O}^{-2}$ per unit cell $=8 \times \frac{1}{8}+6 \times \frac{1}{2}=4$
No of $\mathrm{Al}^{+3}$ per unit cell $=4 \times \frac{1}{2}=2$
No of $\mathrm{Mn}^{+2}$ per unit cell $=8 \times \frac{1}{8}=1$
$\mathbf{M n A l}_{2} \mathbf{O}_{4}$

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