Sapphire is aluminium oxide. Aluminium oxide crystallizes with aluminium ions in two-third of the oc — Solid State Chemistry Question

💡 Solution & Explanation

Let the number of oxide ions (O) in the close-packed array be $N$. The number of octahedral voids is $N$. Aluminium ions (Al) occupy two-thirds of these voids, so their number is $\frac{2}{3}N$. The ratio of Al:O is $\frac{2}{3}N : N = 2 : 3$. The formula is Al$_2$O$_3$. Therefore, correct answer is A.