The correct order of decreasing bond angles in `H_(2)S, NH_(3), BF_(3)` and `SiH_(4)` is

Options

A. `BF_(3) gt SiH_(4) gt H_(2)S gt NH_(3)`
B. `BF_(3) gt SiH_(4) gt NH_(3) gt H_(2)S`
C. `BF_(3) gt NH_(3) gt SiH_(4) gt H_(2)S`
D. `SiH_(4) gt BF_(3) gt NH_(3) gt H_(2)S`

Explanation

To determine the correct order of decreasing bond angles in H₂S, NH₃, BF₃, and SiH₄, we will analyze the molecular geometry and hybridization of each compound.

### Step-by-Step Solution:

1. **Identify the Compounds and Their Structures**:
- BF₃ (Boron Trifluoride)
- SiH₄ (Silane)
- NH₃ (Ammonia)
- H₂S (Hydrogen Sulfide)

2. **Determine the Hybridization of Each Compound**:
- **BF₃**: Boron is sp² hybridized (3 bonding pairs, no lone pairs).
- **SiH₄**: Silicon is sp³ hybridized (4 bonding pairs, no lone pairs).
- **NH₃**: Nitrogen is sp³ hybridized (3 bonding pairs, 1 lone pair).
- **H₂S**: Sulfur is sp³ hybridized (2 bonding pairs, 2 lone pairs).

3. **Estimate the Bond Angles**:
- **BF₃**: The bond angle is approximately 120° (due to sp² hybridization).
- **SiH₄**: The bond angle is approximately 109.5° (due to sp³ hybridization).
- **NH₃**: The bond angle is slightly less than 109.5° due to the presence of one lone pair, approximately 107°.
- **H₂S**: The bond angle is significantly reduced due to two lone pairs, approximately 92°.

4. **Rank the Bond Angles**:
- From the above estimates, we can rank the bond angles from highest to lowest:
- BF₃: 120°
- SiH₄: 109.5°
- NH₃: 107°
- H₂S: 92°

5. **Final Order of Decreasing Bond Angles**:
- The correct order of decreasing bond angles is:
- BF₃ > SiH₄ > NH₃ > H₂S

### Conclusion:
The correct answer is option 2: BF₃ (120°) > SiH₄ (109.5°) > NH₃ (107°) > H₂S (approximately 92°).

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