In which of the following molecule/ion all the bonds are not equal?

Options

A. `XeF_(4)`
B. `BF_(4)^(-)`
C. `C_(2)H_(4)`
D. `SiF_(4)`

Explanation

To determine which of the following molecules or ions has bonds that are not all equal, we will analyze each option based on their molecular structures and hybridization.

### Step-by-Step Solution:

1. **Identify the Molecules/Ions**: The given options are:
- \( \text{XeF}_4 \)
- \( \text{BF}_4^- \)
- \( \text{C}_2\text{H}_4 \)
- \( \text{SiF}_4 \)

2. **Analyze \( \text{XeF}_4 \)**:
- **Hybridization**: The central atom is xenon (Xe), which has 8 valence electrons. It forms 4 bonds with fluorine and has 2 lone pairs.
- **Steric Number**: \( 4 \text{ (bonds)} + 2 \text{ (lone pairs)} = 6 \) → Hybridization is \( \text{sp}^3\text{d}^2 \).
- **Geometry**: The geometry is square planar. In a square planar structure, all bond lengths are equal.

3. **Analyze \( \text{BF}_4^- \)**:
- **Hybridization**: The central atom is boron (B) with 3 valence electrons, plus one extra electron from the negative charge, making a total of 4 electrons. It forms 4 bonds with fluorine.
- **Steric Number**: \( 4 \text{ (bonds)} + 0 \text{ (lone pairs)} = 4 \) → Hybridization is \( \text{sp}^3 \).
- **Geometry**: The geometry is tetrahedral. In a tetrahedral structure, all bond lengths are equal.

4. **Analyze \( \text{C}_2\text{H}_4 \)**:
- **Structure**: Ethylene has a double bond between the two carbon atoms and single bonds between carbon and hydrogen.
- **Bond Types**: The carbon-carbon bond is a double bond (1 sigma + 1 pi), while the carbon-hydrogen bonds are single bonds (sigma only).
- **Bond Lengths**: The carbon-carbon bond is shorter than the carbon-hydrogen bonds due to the presence of the double bond, leading to unequal bond lengths.

5. **Analyze \( \text{SiF}_4 \)**:
- **Hybridization**: The central atom is silicon (Si) with 4 valence electrons, forming 4 bonds with fluorine.
- **Steric Number**: \( 4 \text{ (bonds)} + 0 \text{ (lone pairs)} = 4 \) → Hybridization is \( \text{sp}^3 \).
- **Geometry**: The geometry is tetrahedral. In a tetrahedral structure, all bond lengths are equal.

6. **Conclusion**: Among the given options, only \( \text{C}_2\text{H}_4 \) has bonds that are not equal due to the presence of both a double bond and single bonds.

### Final Answer:
The molecule in which all the bonds are not equal is \( \text{C}_2\text{H}_4 \).

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