The pronounced change from non-metallic behaviour and also increase in the basicity of oxides from nitrogen to bismuth in group `15` is principally due to incresing size of the atoms. The ionisation potential of nitrogen is very high on account of its small size. However, ionisation potential decreases regularly on descending the group.
Which one of the following is a strongest base ?

Options

A. `PH_3`
B. `SbH_3`
C. `AsH_3`
D. `NH_3`

Answer

To determine which hydride of group 15 is the strongest base, we can follow these steps:

### Step 1: Identify the Hydrides of Group 15
The hydrides of group 15 elements include:
- NH₃ (Ammonia) from Nitrogen
- PH₃ (Phosphine) from Phosphorus
- AsH₃ (Arsine) from Arsenic
- SbH₃ (Stibine) from Antimony
- BiH₃ (Bismuthine) from Bismuth

### Step 2: Understand Basicity in Terms of Atomic Size
Basicity in hydrides is primarily due to the presence of a lone pair of electrons on the central atom. As we move down the group from nitrogen to bismuth, the size of the central atom increases. This increase in size affects the availability of the lone pair of electrons for donation, which is crucial for basicity.

### Step 3: Analyze the Trend in Basicity
- The basicity of hydrides decreases as we move down the group. This is because:
- The larger the central atom, the less available the lone pair is for bonding or donation.
- Therefore, NH₃ (with nitrogen being the smallest atom) will have the most available lone pair and thus the strongest basic character.

### Step 4: Conclusion
Based on the analysis, NH₃ (Ammonia) is the strongest base among the hydrides of group 15 due to its small atomic size, which allows for better availability of the lone pair of electrons.

### Final Answer
The strongest base among the hydrides of group 15 is **NH₃ (Ammonia)**.

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