In which of the following species the interatomic bond angle is `109^(@)28'` ?

Options

A. `NH_(3),(BF_(4))^(-1)`
B. `(NH_(4))^(+), BF_(3)`
C. `NH_(3), BF_(4)`
D. `(NH_(2))^(-1), BF_(3)`

Explanation

To determine which species has an interatomic bond angle of 109°28', we need to identify the hybridization and molecular geometry of the given species. The bond angle of 109°28' is characteristic of sp³ hybridization, which corresponds to a tetrahedral molecular geometry.

Let's analyze the options step by step:

### Step 1: Identify the hybridization of each species
1. **NH₃ (Ammonia)**:
- NH₃ has one lone pair and three bonding pairs (from three hydrogen atoms).
- The molecular geometry is trigonal pyramidal due to the lone pair, which causes the bond angle to be less than 109.5° (approximately 107°).
- **Hybridization**: sp³ (but not tetrahedral due to lone pair).

2. **BF₄⁻ (Tetrafluoroborate)**:
- BF₄⁻ has four bonding pairs (from four fluorine atoms) and no lone pairs on the central boron atom.
- The molecular geometry is tetrahedral, with a bond angle of 109.5°.
- **Hybridization**: sp³.

3. **BF₃ (Boron Trifluoride)**:
- BF₃ has three bonding pairs and no lone pairs.
- The molecular geometry is trigonal planar, with a bond angle of 120°.
- **Hybridization**: sp².

4. **NH₂⁻ (Amide Ion)**:
- NH₂⁻ has two bonding pairs and one lone pair.
- The molecular geometry is bent, with a bond angle less than 109.5°.
- **Hybridization**: sp³ (but not tetrahedral due to lone pair).

### Step 2: Compare the bond angles
- **NH₃**: Bond angle is approximately 107° (not 109°28').
- **BF₄⁻**: Bond angle is 109.5° (close to 109°28').
- **BF₃**: Bond angle is 120° (not 109°28').
- **NH₂⁻**: Bond angle is less than 109.5° (not 109°28').

### Conclusion:
The species that has an interatomic bond angle closest to 109°28' is **BF₄⁻**.

### Final Answer:
**BF₄⁻** has an interatomic bond angle of approximately 109°28'.

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