Correct order of decreasing boiling points is :

Options

A. `HF gt HI gt HBr gt HCl`
B. `H_(2)O gt H_(2)Te gt H_(2)Se gt H_(2)S`
C. `Br_(2)gt Cl_(2) gt F_(2)`
D. `CH_(4) gt GeH_(4) gt SiH_(4)`

Answer

To determine the correct order of decreasing boiling points among the given compounds, we need to consider the factors that influence boiling points, such as molecular weight, intermolecular forces, and the presence of hydrogen bonding.

### Step-by-Step Solution:

1. **Identify the Compounds**: Let's assume we are comparing the following compounds: HF (hydrogen fluoride), HCl (hydrogen chloride), HBr (hydrogen bromide), and HI (hydrogen iodide).

2. **Consider Molecular Weight**: Generally, the boiling point of a substance increases with an increase in molecular weight. The molecular weights of the compounds are as follows:
- HF = 20 g/mol
- HCl = 36.5 g/mol
- HBr = 80 g/mol
- HI = 127 g/mol

3. **Evaluate Intermolecular Forces**:
- HF exhibits hydrogen bonding due to the high electronegativity of fluorine, which creates a strong dipole-dipole interaction.
- HCl, HBr, and HI primarily exhibit van der Waals forces (dispersion forces) which are weaker than hydrogen bonds.

4. **Rank the Compounds by Boiling Point**:
- HF has a boiling point of about 20°C, which is higher due to hydrogen bonding.
- HI has the highest molecular weight and thus a higher boiling point (approximately 13.1°C).
- HBr has a boiling point of about -66.8°C.
- HCl has a boiling point of about -85°C.

5. **Conclusion**: Considering both molecular weight and the presence of hydrogen bonding:
- The correct order of decreasing boiling points is: **HF > HI > HBr > HCl**.

### Final Order:
- **HF > HI > HBr > HCl**