Which of the following pairs of species are isostructural ?

Options

A. `SO_(4)^(2-) and BF_(4)^(-)`
B. `NH_(3) and NH_(4)^(+)`
C. `CO_(3)^(2-) and CO_(2)`
D. `CH_(4) and BF_(3)`

Explanation

To determine which pairs of species are isostructural, we need to analyze the hybridization and molecular geometry of each species provided in the options. Isostructural species have the same molecular structure, which is often indicated by the same hybridization and geometry.

### Step-by-Step Solution:

1. **Identify the Species**:
We have the following pairs to analyze:
- SO4^2- and BF4^-
- NH3 and NH4^+
- CO3^2- and CO2
- CH4 and BF3

2. **Analyze SO4^2- and BF4^-**:
- **SO4^2-**: Sulfur (S) is the central atom. It forms four bonds with oxygen (O) atoms. The hybridization is sp3 (four sigma bonds, no lone pairs). The geometry is tetrahedral.
- **BF4^-**: Boron (B) is the central atom. It also forms four bonds with fluorine (F) atoms. The hybridization is sp3 (four sigma bonds, no lone pairs). The geometry is also tetrahedral.
- **Conclusion**: Both SO4^2- and BF4^- are tetrahedral and thus are isostructural.

3. **Analyze NH3 and NH4^+**:
- **NH3**: Nitrogen (N) is the central atom. It forms three bonds with hydrogen (H) atoms and has one lone pair. The hybridization is sp3, but the shape is trigonal pyramidal due to the lone pair.
- **NH4^+**: Nitrogen (N) forms four bonds with hydrogen (H) atoms and has no lone pairs. The hybridization is sp3, and the geometry is tetrahedral.
- **Conclusion**: NH3 is trigonal pyramidal, while NH4^+ is tetrahedral. They are not isostructural.

4. **Analyze CO3^2- and CO2**:
- **CO3^2-**: Carbon (C) is the central atom. It forms three bonds (one double bond with one O and two single bonds with two O's). The hybridization is sp2, and the geometry is trigonal planar.
- **CO2**: Carbon (C) forms two double bonds with oxygen (O) atoms. The hybridization is sp, and the geometry is linear.
- **Conclusion**: CO3^2- is trigonal planar, while CO2 is linear. They are not isostructural.

5. **Analyze CH4 and BF3**:
- **CH4**: Carbon (C) is the central atom. It forms four bonds with hydrogen (H) atoms. The hybridization is sp3, and the geometry is tetrahedral.
- **BF3**: Boron (B) is the central atom. It forms three bonds with fluorine (F) atoms. The hybridization is sp2, and the geometry is trigonal planar.
- **Conclusion**: CH4 is tetrahedral, while BF3 is trigonal planar. They are not isostructural.

### Final Answer:
The only pair of species that are isostructural is **SO4^2- and BF4^-**.