The correct order of bond angle among `H_2S,NH_3,BF_3 and SiH_4` is :

Options

A. `H_2s lt NH_3 lt BF_3 lt SiH_4`
B. `NH_3 lt H_2S lt SiH_4 lt BF_3`
C. `H_2S lt NH_3 lt SiH_4 lt BF_3`
D. `H_2S lt SiH_4 lt NH_3 lt BF_3`.

Answer

To determine the correct order of bond angles among H₂S, NH₃, BF₃, and SiH₄, we need to analyze the molecular geometry and the presence of lone pairs in each molecule.

### Step-by-Step Solution:

1. **Identify the Molecular Geometry:**
- **H₂S (Hydrogen Sulfide):** H₂S has a bent shape due to the presence of two lone pairs on the sulfur atom. The bond angle is approximately 92°.
- **NH₃ (Ammonia):** NH₃ has a trigonal pyramidal shape because of one lone pair on the nitrogen atom. The bond angle is approximately 107°.
- **BF₃ (Boron Trifluoride):** BF₃ has a trigonal planar shape with no lone pairs on the boron atom. The bond angle is approximately 120°.
- **SiH₄ (Silane):** SiH₄ has a tetrahedral shape with no lone pairs on the silicon atom. The bond angle is approximately 109.5°.

2. **Analyze the Bond Angles:**
- H₂S: ~92°
- NH₃: ~107°
- SiH₄: ~109.5°
- BF₃: ~120°

3. **Order the Bond Angles:**
- The bond angles can be ordered from smallest to largest:
- H₂S (92°) < NH₃ (107°) < SiH₄ (109.5°) < BF₃ (120°)

4. **Final Order:**
- Therefore, the correct order of bond angles among H₂S, NH₃, BF₃, and SiH₄ is:
- **H₂S < NH₃ < SiH₄ < BF₃**