Of the three molecules `XeF_4, SF_4, SiF_4` one which have tetrahedral structures is

Options

A. All of three
B. Only `SiF_4`
C. Both `SF_4 and XeF_4`
D. Only `SF_4 and XeF_4`.

Answer

To determine which of the three molecules \( \text{XeF}_4, \text{SF}_4, \text{SiF}_4 \) has a tetrahedral structure, we will analyze each molecule based on its valence electrons, bonding, and geometry.

### Step-by-Step Solution:

1. **Analyze \( \text{XeF}_4 \)**:
- **Valence Electrons**: Xenon (Xe) is a noble gas and has 8 valence electrons. Each fluorine (F) has 7 valence electrons, and there are 4 fluorine atoms contributing \( 4 \times 7 = 28 \) electrons.
- **Total Valence Electrons**: \( 8 + 28 = 36 \) electrons.
- **Bonding**: Xenon forms 4 sigma bonds with 4 fluorine atoms. This uses up \( 4 \times 2 = 8 \) electrons.
- **Lone Pairs**: The remaining electrons are \( 36 - 8 = 28 \) electrons, which correspond to 14 pairs. Since 4 bonds are formed, there are 2 lone pairs left on xenon.
- **Steric Number**: The steric number is the sum of sigma bonds and lone pairs: \( 4 \text{ (bonds)} + 2 \text{ (lone pairs)} = 6 \).
- **Hybridization**: The hybridization is \( \text{sp}^3\text{d}^2 \).
- **Geometry**: The molecular geometry is square planar due to the presence of 2 lone pairs.

2. **Analyze \( \text{SF}_4 \)**:
- **Valence Electrons**: Sulfur (S) has 6 valence electrons. The 4 fluorine atoms contribute \( 4 \times 7 = 28 \) electrons.
- **Total Valence Electrons**: \( 6 + 28 = 34 \) electrons.
- **Bonding**: Sulfur forms 4 sigma bonds with 4 fluorine atoms, using \( 4 \times 2 = 8 \) electrons.
- **Lone Pairs**: The remaining electrons are \( 34 - 8 = 26 \) electrons, which correspond to 13 pairs. Since 4 bonds are formed, there is 1 lone pair left on sulfur.
- **Steric Number**: The steric number is \( 4 \text{ (bonds)} + 1 \text{ (lone pair)} = 5 \).
- **Hybridization**: The hybridization is \( \text{sp}^3\text{d} \).
- **Geometry**: The molecular geometry is trigonal bipyramidal, and the shape is seesaw due to the lone pair.

3. **Analyze \( \text{SiF}_4 \)**:
- **Valence Electrons**: Silicon (Si) has 4 valence electrons. The 4 fluorine atoms contribute \( 4 \times 7 = 28 \) electrons.
- **Total Valence Electrons**: \( 4 + 28 = 32 \) electrons.
- **Bonding**: Silicon forms 4 sigma bonds with 4 fluorine atoms, using \( 4 \times 2 = 8 \) electrons.
- **Lone Pairs**: The remaining electrons are \( 32 - 8 = 24 \) electrons, which correspond to 12 pairs. Since 4 bonds are formed, there are no lone pairs left on silicon.
- **Steric Number**: The steric number is \( 4 \text{ (bonds)} + 0 \text{ (lone pairs)} = 4 \).
- **Hybridization**: The hybridization is \( \text{sp}^3 \).
- **Geometry**: The molecular geometry is tetrahedral.

### Conclusion:
Among the three molecules, only \( \text{SiF}_4 \) has a tetrahedral structure.

### Final Answer:
The molecule with a tetrahedral structure is \( \text{SiF}_4 \).