Which of the following would have permanent dipple moment ?

Options

A. `BF_(3)`
B. `SF_(4)`
C. `SiF_(4)`
D. `XeF_(4)`

Answer

To determine which of the given molecules has a permanent dipole moment, we need to analyze the molecular geometry and the electronegativity of the atoms involved. A permanent dipole moment occurs when there is an uneven distribution of electron density, leading to a separation of charges within the molecule.

### Step-by-Step Solution:

1. **Understanding Dipole Moment**: A dipole moment arises due to the difference in electronegativity between atoms in a molecule. When one atom is more electronegative than another, it attracts the shared electrons more strongly, creating a partial negative charge (δ-) on the more electronegative atom and a partial positive charge (δ+) on the less electronegative atom.

2. **Analyzing Molecules**:
- **BF3 (Boron Trifluoride)**: Boron is less electronegative than fluorine. The three fluorine atoms pull electron density towards themselves, but due to the trigonal planar geometry, the dipole moments cancel each other out. Therefore, BF3 has a dipole moment of zero.

- **SiF4 (Silicon Tetrafluoride)**: Similar to BF3, silicon is less electronegative than fluorine. The tetrahedral shape of SiF4 also leads to the cancellation of dipole moments, resulting in a dipole moment of zero.

- **SF4 (Sulfur Tetrafluoride)**: In SF4, sulfur is less electronegative than fluorine. The molecular geometry is see-saw due to the presence of one lone pair on sulfur. The dipole moments do not cancel out completely, leading to a permanent dipole moment.

- **XeF4 (Xenon Tetrafluoride)**: Xenon is a noble gas and is less electronegative than fluorine. The molecular geometry is square planar, and although there are dipole moments from the fluorine atoms, they cancel each other out due to symmetry. Thus, XeF4 has a dipole moment of zero.

3. **Conclusion**: Among the given molecules, **SF4** has a permanent dipole moment due to its molecular geometry and the presence of a lone pair on sulfur, which prevents the cancellation of dipole moments.

### Final Answer:
**SF4** has a permanent dipole moment.