Which of the following would have permanent dipple moment ?

Options

A. `BF_3`
B. `SiF_4`
C. `SF_4`
D. `XeF_4`

Explanation

To determine which of the given compounds has a permanent dipole moment, we will analyze each option based on their molecular geometry and the presence of lone pairs.

### Step-by-Step Solution:

1. **Analyze BF3 (Boron Trifluoride)**:
- Boron has 3 valence electrons and forms 3 bonds with fluorine atoms.
- The molecular geometry is trigonal planar.
- The bond angles are 120 degrees, and the three dipole moments from the B-F bonds cancel each other out.
- **Conclusion**: BF3 has a net dipole moment of zero.

2. **Analyze SiF4 (Silicon Tetrafluoride)**:
- Silicon has 4 valence electrons and forms 4 bonds with fluorine atoms.
- The molecular geometry is tetrahedral.
- The bond angles are approximately 109.5 degrees, and the four dipole moments from the Si-F bonds also cancel each other out.
- **Conclusion**: SiF4 has a net dipole moment of zero.

3. **Analyze SF4 (Sulfur Tetrafluoride)**:
- Sulfur has 6 valence electrons and forms 4 bonds with fluorine atoms.
- There is 1 lone pair on the sulfur atom.
- The molecular geometry is see-saw due to the presence of the lone pair.
- The lone pair creates an asymmetrical distribution of charge, leading to a net dipole moment.
- **Conclusion**: SF4 has a permanent dipole moment.

4. **Analyze XCF4 (where X can be any element like Xe)**:
- X has 8 valence electrons and forms 4 bonds with fluorine atoms.
- There are 2 lone pairs on the central atom.
- The molecular geometry is square planar.
- The bond pairs are symmetrically arranged in the same plane, and the lone pairs cancel each other's effect.
- **Conclusion**: XCF4 has a net dipole moment of zero.

### Final Answer:
The compound that has a permanent dipole moment is **SF4**.