Which of the following two are isostructural ?

Options

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

Explanation

To determine which of the given pairs of compounds are isostructural, we need to analyze their molecular geometries and steric numbers. Isostructural compounds have the same shape or geometry.

### Step-by-Step Solution:

1. **Identify the Compounds**:
We have the following pairs to analyze:
- Option 1: XEF2 and IF2^-
- Option 2: NH3 and BF3
- Option 3: SO3^2- and CO3^2-
- Option 4: PCl5 and ICl5

2. **Analyze the First Pair (XEF2 and IF2^-)**:
- **XEF2**:
- Valence electrons of X = 8 (assumed) + 2 from 2 fluorine atoms = 10 total.
- Bond pairs = 2 (from 2 F atoms).
- Lone pairs = 3 (since 10 - 2 = 8, and 8/2 = 4, 4 - 2 = 2).
- Steric number = 5 (2 bond pairs + 3 lone pairs).
- Hybridization = sp3d.
- Geometry = trigonal bipyramidal.
- Shape = linear due to lone pairs occupying equatorial positions.

- **IF2^-**:
- Valence electrons of I = 7 + 1 (for the negative charge) + 2 from 2 fluorine atoms = 10 total.
- Bond pairs = 2 (from 2 F atoms).
- Lone pairs = 3 (similar calculation as above).
- Steric number = 5.
- Hybridization = sp3d.
- Geometry = trigonal bipyramidal.
- Shape = linear.

**Conclusion**: XEF2 and IF2^- are isostructural.

3. **Analyze the Second Pair (NH3 and BF3)**:
- **NH3**:
- Valence electrons of N = 5 + 3 from 3 H atoms = 8 total.
- Bond pairs = 3 (from 3 H atoms).
- Lone pairs = 1.
- Steric number = 4.
- Hybridization = sp3.
- Geometry = tetrahedral.
- Shape = trigonal pyramidal.

- **BF3**:
- Valence electrons of B = 3 + 3 from 3 F atoms = 6 total.
- Bond pairs = 3 (from 3 F atoms).
- Lone pairs = 0.
- Steric number = 3.
- Hybridization = sp2.
- Geometry = trigonal planar.
- Shape = trigonal planar.

**Conclusion**: NH3 and BF3 are not isostructural.

4. **Analyze the Third Pair (SO3^2- and CO3^2-)**:
- **SO3^2-**:
- Valence electrons of S = 6 + 3 from 3 O atoms = 9 total + 2 (for the charge) = 11 total.
- Bond pairs = 3 (from 3 O atoms).
- Lone pairs = 1.
- Steric number = 4.
- Hybridization = sp3.
- Geometry = tetrahedral.
- Shape = trigonal pyramidal.

- **CO3^2-**:
- Valence electrons of C = 4 + 3 from 3 O atoms = 7 total + 4 (for the charge) = 10 total.
- Bond pairs = 3 (from 3 O atoms).
- Lone pairs = 0.
- Steric number = 3.
- Hybridization = sp2.
- Geometry = trigonal planar.
- Shape = trigonal planar.

**Conclusion**: SO3^2- and CO3^2- are not isostructural.

5. **Analyze the Fourth Pair (PCl5 and ICl5)**:
- **PCl5**:
- Valence electrons of P = 5 + 5 from 5 Cl atoms = 10 total.
- Bond pairs = 5 (from 5 Cl atoms).
- Lone pairs = 0.
- Steric number = 5.
- Hybridization = sp3d.
- Geometry = trigonal bipyramidal.
- Shape = trigonal bipyramidal.

- **ICl5**:
- Valence electrons of I = 7 + 5 from 5 Cl atoms = 12 total.
- Bond pairs = 5 (from 5 Cl atoms).
- Lone pairs = 1 (since 12 - 10 = 2, and 2/2 = 1).
- Steric number = 6.
- Hybridization = sp3d2.
- Geometry = octahedral.
- Shape = square pyramidal.

**Conclusion**: PCl5 and ICl5 are not isostructural.

### Final Answer:
The isostructural compounds are **XEF2 and IF2^-**.