Among given species identify the isostructural pairs :

Options

A. `[NF_(3) and BF_(3)]`
B. `[BF_(4)^(-) and NH_(4)^(+)]`
C. `[BCl_(3) and BrCl_(3)]`
D. `[NH_(3) and NO_(3)^(-)]`

Explanation

To identify the isostructural pairs among the given species, we need to analyze the molecular geometry and hybridization of each species. Isostructural pairs are those that have the same structure and geometry.

### Step-by-Step Solution:

1. **Identify the first pair: NF3 and BF3**
- **NF3**:
- Nitrogen has 1 lone pair and 3 sigma bonds (with 3 fluorine atoms).
- Steric number = 3 (sigma bonds) + 1 (lone pair) = 4.
- Hybridization = sp³.
- Geometry: Tetrahedral; Shape: Pyramidal.
- **BF3**:
- Boron has no lone pairs and 3 sigma bonds (with 3 fluorine atoms).
- Steric number = 3 (sigma bonds) + 0 (lone pairs) = 3.
- Hybridization = sp².
- Geometry: Trigonal planar.
- **Conclusion**: NF3 and BF3 are not isostructural.

2. **Identify the second pair: BF4⁻ and NH4⁺**
- **BF4⁻**:
- Boron has no lone pairs and 4 sigma bonds (with 4 fluorine atoms).
- Steric number = 4 (sigma bonds) + 0 (lone pairs) = 4.
- Hybridization = sp³.
- Geometry: Tetrahedral.
- **NH4⁺**:
- Nitrogen has no lone pairs and 4 sigma bonds (with 4 hydrogen atoms).
- Steric number = 4 (sigma bonds) + 0 (lone pairs) = 4.
- Hybridization = sp³.
- Geometry: Tetrahedral.
- **Conclusion**: BF4⁻ and NH4⁺ are isostructural.

3. **Identify the third pair: BCl3 and BrCl3**
- **BCl3**:
- Boron has no lone pairs and 3 sigma bonds (with 3 chlorine atoms).
- Steric number = 3 (sigma bonds) + 0 (lone pairs) = 3.
- Hybridization = sp².
- Geometry: Trigonal planar.
- **BrCl3**:
- Bromine has 3 sigma bonds (with 3 chlorine atoms) and 2 lone pairs.
- Steric number = 3 (sigma bonds) + 2 (lone pairs) = 5.
- Hybridization = sp³d.
- Geometry: T-shaped.
- **Conclusion**: BCl3 and BrCl3 are not isostructural.

4. **Identify the fourth pair: NH3 and NO3⁻**
- **NH3**:
- Nitrogen has 1 lone pair and 3 sigma bonds (with 3 hydrogen atoms).
- Steric number = 3 (sigma bonds) + 1 (lone pair) = 4.
- Hybridization = sp³.
- Geometry: Tetrahedral; Shape: Pyramidal.
- **NO3⁻**:
- Nitrogen has 3 sigma bonds (with 3 oxygen atoms) and no lone pairs.
- Steric number = 3 (sigma bonds) + 0 (lone pairs) = 3.
- Hybridization = sp².
- Geometry: Trigonal planar.
- **Conclusion**: NH3 and NO3⁻ are not isostructural.

### Final Conclusion:
The only isostructural pair among the given species is **BF4⁻ and NH4⁺**.