In aluminium oxide, the oxide ions are arranged in hexagonal close packed (hcp) arrangement and the aluminium occupy `2//3` of octahedral voids. What is the formula of oxide ?

Answer

`Al_2O_3`

Explanation

Number of octahedral sites corresponding to each atom in hcp=1
Number of oxygen (O) atoms = 1
It is given that `2//3` of the octahedral sites are occupied by aluminium ions.
Hence, for each oxide ion, there will be `2//3` aluminium ions. so, number of Al atoms = `2//3`
Hence, the formula of the oxide = `Al_(2//3) O_1` or `Al_2O_3`