Which of the following has a geometry different from the other three species (having the same geometry) ?

Options

A. `BF_(4)^(-)`
B. `SO_(4)^(2-)`
C. `XeF_(4)`
D. `PH_(4)^(+)`

Explanation

To determine which of the given species has a geometry different from the others, we will analyze the geometries of each compound step-by-step.

### Step 1: Analyze BF4⁻ (Boron Tetrafluoride Ion)
1. **Central Atom**: Boron (B)
2. **Valence Electrons**: Boron has 3 valence electrons.
3. **Bonds**: In BF4⁻, boron forms 4 bonds with fluorine atoms. Since boron can only accommodate 3 electrons normally, it accepts an electron from one of the fluorine atoms, resulting in a negative charge.
4. **Steric Number Calculation**:
- Sigma bonds: 4 (one for each B-F bond)
- Lone pairs: 0
- Steric Number = 4 + 0 = 4
5. **Hybridization**: sp³
6. **Geometry**: Tetrahedral

### Step 2: Analyze SO4²⁻ (Sulfate Ion)
1. **Central Atom**: Sulfur (S)
2. **Valence Electrons**: Sulfur has 6 valence electrons.
3. **Bonds**: In SO4²⁻, sulfur forms 4 bonds with oxygen atoms (two double bonds and two single bonds with negative charges).
4. **Steric Number Calculation**:
- Sigma bonds: 4 (one for each S-O bond)
- Lone pairs: 0
- Steric Number = 4 + 0 = 4
5. **Hybridization**: sp³
6. **Geometry**: Tetrahedral

### Step 3: Analyze XeF4 (Xenon Tetrafluoride)
1. **Central Atom**: Xenon (Xe)
2. **Valence Electrons**: Xenon has 8 valence electrons.
3. **Bonds**: In XeF4, xenon forms 4 bonds with fluorine atoms and has 2 lone pairs of electrons.
4. **Steric Number Calculation**:
- Sigma bonds: 4 (one for each Xe-F bond)
- Lone pairs: 2
- Steric Number = 4 + 2 = 6
5. **Hybridization**: sp³d²
6. **Geometry**: Octahedral (Shape: Square Planar due to lone pairs)

### Step 4: Analyze PH4⁺ (Phosphonium Ion)
1. **Central Atom**: Phosphorus (P)
2. **Valence Electrons**: Phosphorus has 5 valence electrons.
3. **Bonds**: In PH4⁺, phosphorus forms 4 bonds with hydrogen atoms and carries a positive charge.
4. **Steric Number Calculation**:
- Sigma bonds: 4 (one for each P-H bond)
- Lone pairs: 0
- Steric Number = 4 + 0 = 4
5. **Hybridization**: sp³
6. **Geometry**: Tetrahedral

### Conclusion
- **BF4⁻**: Tetrahedral
- **SO4²⁻**: Tetrahedral
- **XeF4**: Octahedral (Square Planar shape)
- **PH4⁺**: Tetrahedral

**Final Answer**: The species with a geometry different from the others is **XeF4**.

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