Question

The strongest reducing agent amont the following is:

• A. $\text{NH}_3$
• B. $\text{SbH}_3$
• C. $\text{BiH}_3$
• D. $\text{PH}_3$

Answer 1

Answer: (C)

$\text{BiH}_3$

Answer 2

The reducing strength of hydrides of Group 15 elements increases as we move down the group. This trend can be explained based on the following factors: - As we move down the group, the size of the central atom increases, which weakens the E − H bond (where E is the central atom.) The bond dissociation energy decreases. This makes it easier for the hydride to donate hydrogen (as H$^-$), thereby increasing its reducing power. Among the given options:
NH$_3$ (ammonia) has the strongest N--H bond and, therefore, is the weakest reducing agent.
PH$_3$, SbH$_3$, and BiH$_3$ follow the trend of increasing reducing strength due to weaker bonds as we move down the group.
BiH$_3$ (bismuthine) has the weakest Bi--H bond, making it the strongest reducing agent among the given hydrides.
Conclusion: The strongest reducing agent is BiH$_3$.