Boiling/melting points of the following hydrides follow in order.

Options

A. `SbH_3 gt AsH_3 gt PH_3 lt NH_3`
B. `SbH_3 gt AsH_3 gt PH_3 gt NH_3`
C. `SbH_3 gt AsH_3 lt PH_3 lt NH_3`
D. `SbH_3 lt AsH_3 lt PH_3 lt NH_3`

Answer

To determine the boiling and melting points of the hydrides of group 15 elements (nitrogen family), we will analyze the trend in boiling and melting points as we move down the group from nitrogen (N) to bismuth (Bi). The hydrides we will consider are NH3 (ammonia), PH3 (phosphine), AsH3 (arsine), SbH3 (stibine), and BiH3 (bismuthine).

### Step-by-Step Solution:

1. **Identify the Hydrides**: The hydrides in question are NH3, PH3, AsH3, SbH3, and BiH3.

2. **Understand the Trend**: Generally, as we move down the group from nitrogen to bismuth, the boiling and melting points of the hydrides increase. This is due to the increase in molecular weight and size, which leads to stronger van der Waals forces.

3. **Consider Hydrogen Bonding**: NH3 exhibits hydrogen bonding due to the presence of a highly electronegative nitrogen atom. This results in NH3 having a higher boiling point than expected when compared to PH3, despite PH3 being heavier.

4. **Compare the Hydrides**:
- NH3 has a boiling point higher than PH3 due to hydrogen bonding.
- PH3 has a higher boiling point than AsH3, which in turn has a higher boiling point than SbH3.
- SbH3 has a higher boiling point than BiH3.

5. **Order the Boiling Points**:
- NH3 > PH3 > AsH3 > SbH3 > BiH3

6. **Final Conclusion**: The boiling points of the hydrides follow the order:
- NH3 > PH3 > AsH3 > SbH3 > BiH3