Why is `BiH_3` the strongest reducing agent amongst all the hydrides of group 15 elements?

Explanation

To understand why \( \text{BiH}_3 \) is the strongest reducing agent among all the hydrides of group 15 elements, we can break down the explanation into several steps:

### Step 1: Identify the Group 15 Hydrides
Group 15 elements include nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). The hydrides corresponding to these elements are:
- \( \text{NH}_3 \) (Ammonia)
- \( \text{PH}_3 \) (Phosphine)
- \( \text{AsH}_3 \) (Arsine)
- \( \text{SbH}_3 \) (Stibine)
...