The least stable hydride of 15th group is

Options

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

Answer

To determine the least stable hydride of the 15th group, we will analyze the hydrides of the elements in this group: nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi).

### Step-by-Step Solution:

1. **Identify the Hydrides**: The hydrides of the 15th group elements are:
- Nitrogen: Ammonia (NH₃)
- Phosphorus: Phosphine (PH₃)
- Arsenic: Arsenic Hydride (AsH₃)
- Antimony: Antimony Hydride (SbH₃)
- Bismuth: Bismuth Hydride (BiH₃)

2. **Understand Stability Trends**: The stability of these hydrides generally decreases as we move down the group. This is due to the increasing size of the central atom and the decreasing ability to form strong bonds with hydrogen.

3. **Analyze Each Hydride**:
- **NH₃ (Ammonia)**: Very stable due to the small size of nitrogen and strong hydrogen bonding.
- **PH₃ (Phosphine)**: Less stable than NH₃ but more stable than the heavier hydrides.
- **AsH₃ (Arsenic Hydride)**: Even less stable than PH₃.
- **SbH₃ (Antimony Hydride)**: Less stable than AsH₃.
- **BiH₃ (Bismuth Hydride)**: The least stable due to the large size of bismuth, which leads to weaker bonding with hydrogen.

4. **Conclusion**: Based on the stability trend, the least stable hydride in the 15th group is BiH₃ (Bismuth Hydride).

### Final Answer:
The least stable hydride of the 15th group is **BiH₃ (Bismuth Hydride)**.

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