In a normal spinel structure , `O^(2-)` ions form fcc packing and 1/8 of the tetrahedral sites are occupied by divalent metal , `A^(2+)` ions and half of the octahedral sites are occupied by trivalent metal `B^(3+)` ions, what is the ratio of tetrahedral/octahedral sites :
(i) occupied in spinel structure
(ii) not occupied in spinel structure .

Explanation

To solve the problem, we need to analyze the normal spinel structure and calculate the ratio of occupied and unoccupied tetrahedral and octahedral sites.

### Step-by-Step Solution:

1. **Understanding the Structure**:
- In a normal spinel structure, the oxide ions \( O^{2-} \) form a face-centered cubic (FCC) lattice.
- The formula for normal spinel is \( AB_2O_4 \), where:
- \( A^{2+} \) ions occupy tetrahedral sites.
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