To determine which molecule has a fluorite structure, we will analyze each of the given options: LiO2, CaF2, PbO2, and K2O.
### Step-by-Step Solution:
1. **Understanding Fluorite Structure**:
- The fluorite structure is characterized by a face-centered cubic (FCC) arrangement of cations, with anions occupying all the tetrahedral voids. In this structure, the cation is typically larger than the anion.
2. **Analyzing LiO2**:
- Lithium oxide (LiO2) has an anti-fluorite structure. In this structure, the lithium ions occupy all the tetrahedral voids in a face-centered cubic lattice formed by oxide ions. Therefore, LiO2 does not have a fluorite structure.
3. **Analyzing CaF2**:
- Calcium fluoride (CaF2) exhibits a fluorite structure. In this case, calcium ions (Ca²⁺) occupy the face-centered cubic lattice, while fluoride ions (F⁻) occupy all the tetrahedral voids. Thus, CaF2 has a fluorite structure.
4. **Analyzing PbO2**:
- Lead dioxide (PbO2) has a structure similar to the zinc sulfide (ZnS) structure, which is a type of sphalerite structure. In this structure, the oxide ions form an FCC lattice, and the lead ions occupy the tetrahedral voids. Therefore, PbO2 does not have a fluorite structure.
5. **Analyzing K2O**:
- Potassium oxide (K2O) typically adopts a structure similar to sodium chloride (NaCl), which is a simple cubic structure. The potassium ions occupy the lattice points, while oxide ions occupy the octahedral voids. Thus, K2O does not have a fluorite structure.
### Conclusion:
From the analysis above, the only compound that has a fluorite structure is **CaF2**.
### Final Answer:
CaF2
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