A stronger reducing agent is

Options

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

Answer

To determine which of the given substances is a stronger reducing agent among ammonia (NH₃), phosphorus (P), phosphine (PH₃), SbS₃, and BiS₃, we can analyze the properties of these compounds based on their ability to donate electrons or hydrogen.

### Step-by-Step Solution:

1. **Understanding Reducing Agents**:
A reducing agent is a substance that can donate electrons or supply hydrogen to another substance, thereby reducing it.

2. **Identify the Compounds**:
The compounds in question are:
- Ammonia (NH₃)
- Phosphorus (P)
- Phosphine (PH₃)
- Antimony trisulfide (SbS₃)
- Bismuth trisulfide (BiS₃)

3. **Group 15 Elements**:
These compounds are derived from group 15 elements (nitrogen, phosphorus, arsenic, antimony, and bismuth). As we move down the group, the size of the atoms increases.

4. **Bond Length and Strength**:
As the size of the central atom increases, the bond length of the hydrides also increases. For example:
- NH₃ (shortest bond length)
- PH₃
- SbH₃
- BiH₃ (longest bond length)

Longer bonds are generally weaker, meaning they can break more easily, allowing for the release of hydrogen.

5. **Comparing Hydrides**:
- NH₃ has strong N-H bonds and is not a strong reducing agent.
- PH₃ has weaker P-H bonds than NH₃ but is still not as strong a reducing agent as BiH₃.
- SbH₃ has even weaker bonds than PH₃.
- BiH₃ has the weakest bonds among these due to the largest atomic size, making it the most capable of donating hydrogen.

6. **Conclusion**:
Since BiH₃ has the weakest bonds, it can easily break and supply hydrogen for reduction, making it the strongest reducing agent among the options provided.

### Final Answer:
The stronger reducing agent is **BiH₃** (Bismuth trisulfide).

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