The number of molecules with pyramidal shape are :
`NH_(3), ClF_(3), SO_(3), PCl_(3), XeO_(3), BCl_(3), ClO_(3)^(-), SO_(3)^(2-)`

Options

A. 5
B. 4
C. 3
D. 6

Answer

To determine the number of molecules with a pyramidal shape among the given options, we need to analyze the hybridization and the arrangement of bond pairs and lone pairs for each molecule. A pyramidal shape typically arises when there are three bond pairs and one lone pair (sp³ hybridization).

### Step-by-Step Solution:

1. **NH₃ (Ammonia)**:
- Nitrogen (N) has 5 valence electrons.
- It forms 3 bonds with hydrogen (H) and has 1 lone pair.
- Steric number = 3 (bond pairs) + 1 (lone pair) = 4.
- Hybridization: sp³.
- Shape: Pyramidal.
- **Conclusion**: NH₃ has a pyramidal shape.

2. **ClF₃ (Chlorine trifluoride)**:
- Chlorine (Cl) has 7 valence electrons.
- It forms 3 bonds with fluorine (F) and has 2 lone pairs.
- Steric number = 3 (bond pairs) + 2 (lone pairs) = 5.
- Hybridization: sp³d.
- Shape: T-shaped, not pyramidal.
- **Conclusion**: ClF₃ does not have a pyramidal shape.

3. **SO₃ (Sulfur trioxide)**:
- Sulfur (S) has 6 valence electrons.
- It forms 3 double bonds with oxygen (O).
- Steric number = 3 (bond pairs) + 0 (lone pairs) = 3.
- Hybridization: sp².
- Shape: Trigonal planar, not pyramidal.
- **Conclusion**: SO₃ does not have a pyramidal shape.

4. **PCl₃ (Phosphorus trichloride)**:
- Phosphorus (P) has 5 valence electrons.
- It forms 3 bonds with chlorine (Cl) and has 1 lone pair.
- Steric number = 3 (bond pairs) + 1 (lone pair) = 4.
- Hybridization: sp³.
- Shape: Pyramidal.
- **Conclusion**: PCl₃ has a pyramidal shape.

5. **XeO₃ (Xenon trioxide)**:
- Xenon (Xe) has 8 valence electrons.
- It forms 3 bonds with oxygen (O) and has 1 lone pair.
- Steric number = 3 (bond pairs) + 1 (lone pair) = 4.
- Hybridization: sp³.
- Shape: Pyramidal.
- **Conclusion**: XeO₃ has a pyramidal shape.

6. **BCl₃ (Boron trichloride)**:
- Boron (B) has 3 valence electrons.
- It forms 3 bonds with chlorine (Cl) and has 0 lone pairs.
- Steric number = 3 (bond pairs) + 0 (lone pairs) = 3.
- Hybridization: sp².
- Shape: Trigonal planar, not pyramidal.
- **Conclusion**: BCl₃ does not have a pyramidal shape.

7. **ClO₃⁻ (Chlorate ion)**:
- Chlorine (Cl) has 7 valence electrons.
- It forms 3 bonds with oxygen (O) and has 1 lone pair.
- Steric number = 3 (bond pairs) + 1 (lone pair) = 4.
- Hybridization: sp³.
- Shape: Pyramidal.
- **Conclusion**: ClO₃⁻ has a pyramidal shape.

8. **SO₃²⁻ (Sulfite ion)**:
- Sulfur (S) has 6 valence electrons.
- It forms 3 bonds with oxygen (O) and has 1 lone pair.
- Steric number = 3 (bond pairs) + 1 (lone pair) = 4.
- Hybridization: sp³.
- Shape: Pyramidal.
- **Conclusion**: SO₃²⁻ has a pyramidal shape.

### Final Count of Pyramidal Molecules:
- The molecules with a pyramidal shape are: **NH₃, PCl₃, XeO₃, ClO₃⁻, and SO₃²⁻**.
- Total: **5 molecules**.