In which of the following molecules /ions , are all the bonds not equal ?

Options

A. `SF_4`
B. `SiF_4`
C. `XeF_4`
D. `BF_4^-`

Explanation

To determine which of the given molecules or ions have unequal bond lengths or bond strengths, we will analyze each option systematically.

### Step-by-Step Solution:

1. **Identify the Molecules/Ions**:
- We need to analyze the following:
- SF4 (Sulfur Tetrafluoride)
- SiF4 (Silicon Tetrafluoride)
- XeF4 (Xenon Tetrafluoride)
- BF4^- (Boron Tetrafluoride)

2. **Analyze SF4**:
- **Valence Electrons**: Sulfur (S) has 6 valence electrons. In SF4, it shares 4 electrons with 4 fluorine atoms and has 1 lone pair.
- **Hybridization**: The hybridization is sp3d (5 regions of electron density).
- **Molecular Geometry**: The molecular shape is seesaw due to the presence of the lone pair.
- **Bond Types**: There are 2 axial and 2 equatorial fluorine atoms. The axial bonds are longer and weaker than the equatorial bonds due to increased repulsion.
- **Conclusion**: The bonds in SF4 are not equal.

3. **Analyze SiF4**:
- **Valence Electrons**: Silicon (Si) has 4 valence electrons. In SiF4, it shares all 4 electrons with 4 fluorine atoms.
- **Hybridization**: The hybridization is sp3 (4 regions of electron density).
- **Molecular Geometry**: The molecular shape is tetrahedral.
- **Bond Types**: All Si-F bonds are equivalent.
- **Conclusion**: The bonds in SiF4 are equal.

4. **Analyze XeF4**:
- **Valence Electrons**: Xenon (Xe) has 8 valence electrons. In XeF4, it shares 4 electrons with 4 fluorine atoms and has 2 lone pairs.
- **Hybridization**: The hybridization is sp3d2 (6 regions of electron density).
- **Molecular Geometry**: The molecular shape is square planar.
- **Bond Types**: All Xe-F bonds are equivalent.
- **Conclusion**: The bonds in XeF4 are equal.

5. **Analyze BF4^-**:
- **Valence Electrons**: Boron (B) has 3 valence electrons and accepts 1 electron to form BF4^-. It shares 4 electrons with 4 fluorine atoms.
- **Hybridization**: The hybridization is sp3 (4 regions of electron density).
- **Molecular Geometry**: The molecular shape is tetrahedral.
- **Bond Types**: All B-F bonds are equivalent.
- **Conclusion**: The bonds in BF4^- are equal.

### Final Answer:
The molecules/ions in which all the bonds are not equal are:
- **SF4**