Fifth group elements form hydrides to type `AH_(3)`. The hydrides have a lone pair of electrons. The hydries are reducing in nature and the reducing power is related to the stability of A-H bonds. The hydrides are covalent and low boiling. Their boiling points depends on their ability to from hydrogen bond and their molecular size which decide the intermolcular forces in the hydrides .
The boiling points of the hydrides of V-group elements are in the
order :

Options

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

Explanation

To determine the boiling points of the hydrides of the fifth group elements (Group 15), we need to analyze the hydrides formed by these elements: NH₃ (ammonia), PH₃ (phosphine), AsH₃ (arsine), SbH₃ (stibine), and BiH₃ (bismuthine). The boiling points of these hydrides can be influenced by factors such as hydrogen bonding and Van der Waals forces.

### Step-by-Step Solution:

1. **Identify the Hydrides**: The hydrides of the fifth group elements are NH₃, PH₃, AsH₃, SbH₃, and BiH₃.

2. **Consider Hydrogen Bonding**:
- NH₃ can form strong hydrogen bonds due to the high electronegativity of nitrogen compared to hydrogen. This leads to a higher boiling point.
- The other hydrides (PH₃, AsH₃, SbH₃, BiH₃) do not form hydrogen bonds as effectively because the electronegativities of phosphorus, arsenic, antimony, and bismuth are closer to that of hydrogen.

3. **Analyze the Boiling Points**:
- NH₃ has a boiling point of -33.34 °C, which is higher than PH₃ (-87.7 °C) and AsH₃ (-62 °C) due to hydrogen bonding.
- PH₃, AsH₃, SbH₃, and BiH₃ do not exhibit significant hydrogen bonding, and their boiling points will primarily depend on Van der Waals forces.

4. **Consider Molecular Size and Van der Waals Forces**:
- As we move down the group from PH₃ to BiH₃, the molecular size increases, leading to stronger Van der Waals forces due to increased molecular mass.
- Therefore, the boiling points will increase from PH₃ to BiH₃.

5. **Order of Boiling Points**:
- The order of boiling points based on the above analysis is:
- NH₃ > SbH₃ > AsH₃ > PH₃ > BiH₃
- This order reflects the strong hydrogen bonding in NH₃ and the increasing Van der Waals forces in the heavier hydrides.

### Final Order of Boiling Points:
The boiling points of the hydrides of the fifth group elements are in the order:
**NH₃ > SbH₃ > AsH₃ > PH₃ > BiH₃**