Basicity of which of the following hydride is maximum ?

Question

Accepted Answer

The question asks about the basicity of different hydrides, and the correct answer is Option 3: $NH_{3}$ (ammonia). Let's explore why $NH_{3}$ is the most basic among the given options and why the others are less basic.

### Explanation for Option 3: $NH_{3}$

1. **Lone Pair Availability**: Ammonia ($NH_{3}$) has a lone pair of electrons on the nitrogen atom, which is readily available for donation. This makes it a strong Lewis base.

2. **Electronegativity**: Nitrogen is more electronegative than phosphorus, arsenic, and antimony. This higher electronegativity means that nitrogen holds its lone pair less tightly, making it more available for bonding with protons (H+ ions).

3. **Size and Bonding**: The smaller size of the nitrogen atom compared to phosphorus, arsenic, and antimony allows for a more concentrated electron cloud, enhancing its ability to donate the lone pair.

4. **Hydrogen Bonding**: Ammonia can form hydrogen bonds due to its high electronegativity and the presence of hydrogen atoms. This property increases its solubility in water and enhances its basicity in aqueous solutions.

### Explanation for Other Options:

1. **Option 1: $PH_{3}$ (Phosphine)**
   - **Lone Pair Availability**: Phosphorus also has a lone pair, but it is less available for donation compared to nitrogen due to its larger atomic size.
   - **Electronegativity**: Phosphorus is less electronegative than nitrogen, which means it holds its lone pair more tightly, reducing its basicity.
   - **Bonding**: The larger size of phosphorus leads to a more diffuse electron cloud, making the lone pair less concentrated and less available for bonding.

2. **Option 2: $AsH_{3}$ (Arsine)**
   - **Lone Pair Availability**: Arsenic's lone pair is even less available than phosphorus due to its larger size.
   - **Electronegativity**: Arsenic is less electronegative than both nitrogen and phosphorus, further reducing its ability to donate the lone pair.
   - **Bonding**: The electron cloud is more diffuse, and the lone pair is less concentrated, making $AsH_{3}$ a weaker base.

3. **Option 4: $SbH_{3}$ (Stibine)**
   - **Lone Pair Availability**: Antimony has the least available lone pair among the given options due to its large atomic size.
   - **Electronegativity**: Antimony is the least electronegative, meaning it holds its lone pair very tightly, making it the weakest base.
   - **Bonding**: The electron cloud is very diffuse, and the lone pair is not readily available for donation, resulting in very low basicity.

In conclusion, $NH_{3}$ is the most basic hydride among the options due to its high electronegativity, small atomic size, and the availability of its lone pair for donation. The other hydrides have larger atomic sizes, lower electronegativities, and less available lone pairs, making them less basic.