Which of the following is a polar moleule ?

Options

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

Explanation

To determine which of the given molecules is polar, we need to analyze the molecular geometry and the presence of lone pairs, as well as the electronegativity of the atoms involved. Let's break down the analysis step by step.

### Step 1: Analyze SF4
1. **Valence Electrons**: Sulfur (S) has 6 valence electrons, and each Fluorine (F) has 1 valence electron. Thus, SF4 has a total of \(6 + 4 \times 1 = 10\) valence electrons.
2. **Bond Pairs and Lone Pairs**: There are 4 bond pairs (S-F) and 1 lone pair on sulfur.
3. **Steric Number**: The steric number is \(4 + 1 = 5\), indicating SP3D hybridization.
4. **Molecular Geometry**: The geometry is trigonal bipyramidal with one lone pair in the equatorial position.
5. **Dipole Moment**: The dipole moments from the S-F bonds do not cancel out due to the asymmetrical arrangement caused by the lone pair. Thus, SF4 is a polar molecule.

### Step 2: Analyze XeF4
1. **Valence Electrons**: Xenon (Xe) has 8 valence electrons, and each Fluorine has 1. Thus, XeF4 has \(8 + 4 \times 1 = 12\) valence electrons.
2. **Bond Pairs and Lone Pairs**: There are 4 bond pairs and 2 lone pairs on xenon.
3. **Steric Number**: The steric number is \(4 + 2 = 6\), indicating SP3D2 hybridization.
4. **Molecular Geometry**: The geometry is octahedral with two lone pairs opposite each other.
5. **Dipole Moment**: The dipole moments from the S-F bonds cancel out due to the symmetrical arrangement. Thus, XeF4 is a non-polar molecule.

### Step 3: Analyze SiF4
1. **Valence Electrons**: Silicon (Si) has 4 valence electrons, and each Fluorine has 1. Thus, SiF4 has \(4 + 4 \times 1 = 8\) valence electrons.
2. **Bond Pairs and Lone Pairs**: There are 4 bond pairs and no lone pairs.
3. **Steric Number**: The steric number is 4, indicating SP3 hybridization.
4. **Molecular Geometry**: The geometry is tetrahedral.
5. **Dipole Moment**: The dipole moments from the Si-F bonds cancel out due to the symmetrical arrangement. Thus, SiF4 is a non-polar molecule.

### Step 4: Analyze BF3
1. **Valence Electrons**: Boron (B) has 3 valence electrons, and each Fluorine has 1. Thus, BF3 has \(3 + 3 \times 1 = 6\) valence electrons.
2. **Bond Pairs and Lone Pairs**: There are 3 bond pairs and no lone pairs.
3. **Steric Number**: The steric number is 3, indicating SP2 hybridization.
4. **Molecular Geometry**: The geometry is trigonal planar.
5. **Dipole Moment**: The dipole moments from the B-F bonds cancel out due to the symmetrical arrangement. Thus, BF3 is a non-polar molecule.

### Conclusion
From the analysis above, the only polar molecule among the given options is **SF4**.