Of the following hydrides the boiling point is very low for

Options

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

Explanation

To determine which hydride has the lowest boiling point among the group 15 hydrides, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Group 15 Hydrides**: The hydrides of group 15 elements include NH3 (Ammonia), PH3 (Phosphine), AsH3 (Arsine), and SbH3 (Stibine).

2. **Consider Molecular Mass**: Generally, as the molecular mass of a compound increases, the boiling point tends to increase. The molecular masses are approximately:
- NH3: 17 g/mol
- PH3: 34 g/mol
- AsH3: 77 g/mol
- SbH3: 124 g/mol

3. **Analyze Intermolecular Forces**: The presence of intermolecular forces, particularly hydrogen bonding, can significantly affect boiling points. NH3 exhibits strong hydrogen bonding due to the high electronegativity of nitrogen, which leads to a higher boiling point compared to the others.

4. **Evaluate Boiling Points**:
- NH3 has a high boiling point due to hydrogen bonding.
- PH3 has weaker van der Waals forces and no hydrogen bonding, leading to a lower boiling point.
- AsH3 and SbH3 have even higher boiling points due to their larger molecular masses and the presence of metallic bonding.

5. **Order the Boiling Points**: Based on the analysis:
- NH3 > SbH3 > AsH3 > PH3

6. **Conclusion**: The hydride with the lowest boiling point among the group 15 hydrides is **PH3 (Phosphine)**.

### Final Answer:
The boiling point is very low for **PH3 (Phosphine)**.