Which one of the following is the strongest base ?

Options

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

Answer

To determine which of the following hydrides of Group 15 is the strongest base, we need to analyze the basicity of the hydrides: ammonia (NH₃), phosphine (PH₃), arsine (AsH₃), and stibine (SbH₃).

### Step 1: Understand Basicity
Basicity refers to the ability of a compound to donate a pair of electrons (Lewis base) or accept protons (Brønsted base). In the case of hydrides, we are primarily concerned with their ability to donate a lone pair of electrons.

**Hint:** Remember that the stronger the base, the more readily it can donate its lone pair of electrons.

### Step 2: Analyze the Hydrides
- **Ammonia (NH₃)**: The nitrogen atom in ammonia has a small size and a concentrated lone pair of electrons, making it readily available for donation.
- **Phosphine (PH₃)**: The phosphorus atom is larger than nitrogen, which means the lone pair of electrons is more diffuse and less available for donation compared to ammonia.
- **Arsine (AsH₃)**: The arsenic atom is even larger, leading to a further decrease in the availability of the lone pair.
- **Stibine (SbH₃)**: The bismuth atom is the largest in this group, and its lone pair is the least available for donation.

**Hint:** Consider how the size of the central atom affects the availability of the lone pair of electrons.

### Step 3: Compare Basicity
As we move down the group from nitrogen to bismuth, the size of the central atom increases, leading to a decrease in the basicity of the hydrides. This is because the lone pair of electrons becomes less concentrated and more diffuse.

- **NH₃ > PH₃ > AsH₃ > SbH₃** in terms of basic strength.

**Hint:** Recall that smaller atoms with concentrated lone pairs tend to be stronger bases.

### Step 4: Conclusion
From the analysis, we conclude that ammonia (NH₃) is the strongest base among the given hydrides.

**Final Answer:** **Ammonia (NH₃) is the strongest base.**