Melting point of hydrogen of nitrogen family follows the order

Options

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

Answer

To determine the melting point of hydrides in the nitrogen family (Group 15), we need to analyze the trend and the specific properties of each hydride. The hydrides in this family include NH3 (ammonia), PH3 (phosphine), AsH3 (arsine), and SbH3 (stibine).

### Step-by-Step Solution:

1. **Identify the Hydrides**: The hydrides of the nitrogen family we are considering are:
- NH3 (Ammonia)
- PH3 (Phosphine)
- AsH3 (Arsine)
- SbH3 (Stibine)

2. **Understand the General Trend**: Generally, the melting points of hydrides in a group increase as you move down the group in the periodic table. This is due to the increase in molecular size and mass, which leads to stronger van der Waals forces.

3. **Consider Hydrogen Bonding**: NH3 has a higher melting point than expected due to hydrogen bonding. The presence of hydrogen bonds in NH3 requires more energy to break, resulting in a higher melting point compared to the other hydrides.

4. **List the Melting Points**: Based on the above considerations, we can summarize the melting points:
- NH3: Higher melting point due to hydrogen bonding.
- SbH3: Higher melting point than AsH3 and PH3 but lower than NH3.
- AsH3: Lower melting point than SbH3 but higher than PH3.
- PH3: Lowest melting point among these hydrides.

5. **Establish the Order**: Therefore, the correct order of melting points from highest to lowest is:
- NH3 > SbH3 > AsH3 > PH3

6. **Conclusion**: The final order of melting points of the hydrides in the nitrogen family is:
- NH3 > SbH3 > AsH3 > PH3

### Final Answer:
The melting point of hydrides in the nitrogen family follows the order: **NH3 > SbH3 > AsH3 > PH3**.