Which of the following orders of melting point of hybrides of halogens is correct ?

Options

A. `HF gt HCl gt HBr`
B. `HF lt HCl lt HBr`
C. `HF gt HBr gt HCl`
D. `HF lt HCl gt HBr`

Answer

To determine the correct order of melting points of the hydrides of halogens (HF, HCl, HBr), we can analyze the factors affecting their melting points, such as hydrogen bonding and Van der Waals forces.

### Step-by-Step Solution:

1. **Identify the Hydrides**: The hydrides of halogens we are considering are HF (hydrogen fluoride), HCl (hydrogen chloride), and HBr (hydrogen bromide).

2. **Analyze Hydrogen Bonding in HF**:
- HF exhibits strong hydrogen bonding due to the high electronegativity of fluorine. This results in a significant amount of energy required to break these bonds, leading to a higher melting point for HF compared to the other two hydrides.

3. **Consider the Other Hydrides (HCl and HBr)**:
- HCl and HBr do not exhibit hydrogen bonding to the same extent as HF. Instead, they primarily rely on Van der Waals forces for their intermolecular interactions.
- The strength of Van der Waals forces depends on the molar mass of the molecules.

4. **Calculate the Molar Masses**:
- For HCl:
- H = 1 g/mol
- Cl = 35.5 g/mol
- Total = 1 + 35.5 = 36.5 g/mol
- For HBr:
- H = 1 g/mol
- Br = 80 g/mol
- Total = 1 + 80 = 81 g/mol

5. **Compare the Molar Masses**:
- HBr has a higher molar mass (81 g/mol) compared to HCl (36.5 g/mol). Since Van der Waals forces increase with molar mass, HBr will have a higher melting point than HCl.

6. **Determine the Order of Melting Points**:
- Based on the analysis:
- HF has the highest melting point due to hydrogen bonding.
- HBr has a higher melting point than HCl due to its larger molar mass and stronger Van der Waals forces.
- Therefore, the correct order of melting points is:
- **HF > HBr > HCl**

### Final Answer:
The correct order of melting points of the hydrides of halogens is **HF > HBr > HCl**.