Ferric oxide crystalliizes in a hexagonal close-packed array of oxide ions with two out of every three octahedral holes occupied by ferric ions. Derive the formula of the ferric oxide.

Explanation

To derive the formula of ferric oxide (Fe2O3) based on the given information, we can follow these steps:

### Step 1: Determine the number of oxide ions
Let the number of oxide ions be represented as \( X \).

### Step 2: Calculate the number of octahedral voids
In a hexagonal close-packed (hcp) structure, the number of octahedral voids is equal to the number of anions (oxide ions in this case). Therefore, the number of octahedral voids is also \( X \).

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