Which of the following pairs are iso-structural ?

Options

A. `XeF_(2),lF_(2)^(-)`
B. `NH_(3),BF_(3)`
C. `CO_(3)^(2-),SO_(3)^(2-)`
D. `PCl_(5),lCl_(5)`

Explanation

To determine which pairs are iso-structural, we need to analyze the hybridization and molecular geometry of the given compounds. Iso-structural compounds have similar structures and geometries.

### Step-by-Step Solution:

1. **Identify the first pair: XCF2 and IF2-**
- For XCF2:
- Count the valence electrons:
- X (unknown element) contributes 8, C contributes 4, and F contributes 2*7 = 14.
- Total = 8 + 4 + 14 = 26 electrons.
- Calculate hybridization:
- Using the formula: (1/2) * (Valence Electrons + Monovalent Atoms - Charge)
- (1/2) * (8 + 2 + 0) = 5 → sp³d hybridization.
- Determine the molecular geometry:
- 2 bonds and 3 lone pairs → Linear structure.

- For IF2-:
- Count the valence electrons:
- Iodine (I) contributes 7, F contributes 2*7 = 14, and there is an additional electron due to the negative charge.
- Total = 7 + 14 + 1 = 22 electrons.
- Calculate hybridization:
- (1/2) * (7 + 2 + 1) = 5 → sp³d hybridization.
- Determine the molecular geometry:
- 2 bonds and 3 lone pairs → Linear structure.

- Conclusion: Both XCF2 and IF2- are linear and have sp³d hybridization, hence they are iso-structural.

2. **Identify the second pair: PCl5 and SF4**
- For PCl5:
- Count the valence electrons:
- P contributes 5, and Cl contributes 5*7 = 35.
- Total = 5 + 35 = 40 electrons.
- Calculate hybridization:
- (1/2) * (5 + 5 + 0) = 5 → sp³d hybridization.
- Determine the molecular geometry:
- 5 bonds and 0 lone pairs → Trigonal bipyramidal structure.

- For SF4:
- Count the valence electrons:
- S contributes 6, and F contributes 4*7 = 28.
- Total = 6 + 28 = 34 electrons.
- Calculate hybridization:
- (1/2) * (6 + 4 + 0) = 5 → sp³d hybridization.
- Determine the molecular geometry:
- 4 bonds and 1 lone pair → Seesaw structure.

- Conclusion: PCl5 is trigonal bipyramidal, while SF4 is seesaw; they are not iso-structural.

3. **Identify the third pair: CO2 and SO2**
- For CO2:
- Count the valence electrons:
- C contributes 4, and O contributes 2*6 = 12.
- Total = 4 + 12 = 16 electrons.
- Calculate hybridization:
- (1/2) * (4 + 4 + 0) = 4 → sp hybridization.
- Determine the molecular geometry:
- 2 bonds and 0 lone pairs → Linear structure.

- For SO2:
- Count the valence electrons:
- S contributes 6, and O contributes 2*6 = 12.
- Total = 6 + 12 = 18 electrons.
- Calculate hybridization:
- (1/2) * (6 + 4 + 0) = 5 → sp² hybridization.
- Determine the molecular geometry:
- 2 bonds and 1 lone pair → Bent structure.

- Conclusion: CO2 is linear, while SO2 is bent; they are not iso-structural.

4. **Identify the fourth pair: XeF4 and BrF5**
- For XeF4:
- Count the valence electrons:
- Xe contributes 8, and F contributes 4*7 = 28.
- Total = 8 + 28 = 36 electrons.
- Calculate hybridization:
- (1/2) * (8 + 4 + 0) = 6 → sp³d² hybridization.
- Determine the molecular geometry:
- 4 bonds and 2 lone pairs → Square planar structure.

- For BrF5:
- Count the valence electrons:
- Br contributes 7, and F contributes 5*7 = 35.
- Total = 7 + 35 = 42 electrons.
- Calculate hybridization:
- (1/2) * (7 + 5 + 0) = 6 → sp³d² hybridization.
- Determine the molecular geometry:
- 5 bonds and 1 lone pair → Square pyramidal structure.

- Conclusion: XeF4 is square planar, while BrF5 is square pyramidal; they are not iso-structural.

### Final Answer:
The only iso-structural pair is **XCF2 and IF2-**.