The decreasing order of boiling points of the following hydrides is

Options

A. `SbH_(3) gt AsH_(3) gt PH_(3) gt NH_(3)`
B. `NH_(3) gt SbH_(3) gt AsH_(3) gt PH_(3)`
C. `SbH_(3) gt NH_(3) gt AsH_(3) gt PH_(3)`
D. `PH_(3) gt AsH_(3) gt SbH_(3) gt NH_(3)`

Explanation

To determine the decreasing order of boiling points of the given hydrides (NH3, PH3, AsH3, SbH3), we will analyze the factors affecting boiling points, particularly focusing on molecular mass and hydrogen bonding.

### Step-by-Step Solution:

1. **Identify the Hydrides**: The hydrides we are considering are NH3 (Ammonia), PH3 (Phosphine), AsH3 (Arsine), and SbH3 (Stibine).

2. **Understand the Factors Affecting Boiling Points**:
- Boiling points of hydrides generally increase with increasing molecular mass.
- Hydrogen bonding significantly affects the boiling point, especially in NH3, which has strong hydrogen bonds due to the presence of nitrogen.

3. **Determine Molecular Mass**:
- NH3: Molecular mass = 14 (N) + 3(1) (H) = 17 g/mol
- PH3: Molecular mass = 31 (P) + 3(1) (H) = 34 g/mol
- AsH3: Molecular mass = 75 (As) + 3(1) (H) = 78 g/mol
- SbH3: Molecular mass = 121 (Sb) + 3(1) (H) = 124 g/mol

4. **Analyze the Expected Order Based on Molecular Mass**:
- Based on molecular mass alone, the expected order of boiling points (from highest to lowest) would be:
- SbH3 > AsH3 > PH3 > NH3

5. **Consider Hydrogen Bonding**:
- NH3 has strong hydrogen bonding, which significantly raises its boiling point compared to what would be expected based solely on molecular mass.
- Therefore, NH3 will have a higher boiling point than expected.

6. **Revised Order of Boiling Points**:
- Taking into account the strong hydrogen bonding in NH3, the actual order of boiling points becomes:
- SbH3 > NH3 > AsH3 > PH3

7. **Final Conclusion**:
- The correct decreasing order of boiling points for the hydrides is:
- SbH3 > NH3 > AsH3 > PH3

### Answer:
The correct order of boiling points is: **SbH3 > NH3 > AsH3 > PH3**