Which of the following solid has maximum melting points?

Options

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

Answer

To determine which of the following solids has the maximum melting point among NH3 (ammonia), PH3 (phosphine), AsH3 (arsine), and SbH3 (stibine), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Compounds**: We have four compounds to consider:
- NH3 (Ammonia)
- PH3 (Phosphine)
- AsH3 (Arsine)
- SbH3 (Stibine)

2. **Understand the Nature of the Compounds**: All these compounds are hydrides of group 15 elements. They are molecular solids at room temperature.

3. **Consider the Factors Affecting Melting Points**: The melting point of a solid is influenced by the strength of intermolecular forces present in the solid. The main types of intermolecular forces are:
- Hydrogen bonding
- Dipole-dipole interactions
- Van der Waals forces

4. **Analyze NH3**:
- NH3 is known to form strong hydrogen bonds due to the presence of nitrogen, which is highly electronegative.
- The hydrogen bonds in NH3 are significantly stronger than the other types of intermolecular forces present in the other hydrides.

5. **Analyze the Other Compounds (PH3, AsH3, SbH3)**:
- PH3, AsH3, and SbH3 do not form hydrogen bonds as effectively as NH3 because phosphorus, arsenic, and antimony are less electronegative compared to nitrogen.
- As we move down the group from nitrogen to phosphorus to arsenic to antimony, the ability to form hydrogen bonds decreases due to decreasing electronegativity and increasing atomic size.

6. **Conclusion**:
- Since NH3 has strong hydrogen bonding, while PH3, AsH3, and SbH3 have weaker van der Waals forces, NH3 will have the highest melting point among the given compounds.

7. **Final Answer**: The solid with the maximum melting point is **NH3 (Ammonia)**.