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 for the given compounds, we will analyze each option based on the presence of hydrogen bonding and the molecular mass of the compounds.

### Step-by-Step Solution:

1. **Identify Compounds and Their Properties**:
- We have four sets of compounds to analyze: HF, HI, HBr, HCl; H2O, H2Te, H2Se, H2S; Br2, Cl2, F2; CH4, SiH4, GeH4.

2. **Analyze the First Set: HF, HI, HBr, HCl**:
- HF has hydrogen bonding due to the presence of highly electronegative fluorine. This results in a higher boiling point.
- HI, HBr, and HCl do not exhibit hydrogen bonding but have Van der Waals forces. The boiling points will depend on their molecular masses.
- Order based on boiling points: HF > HI > HBr > HCl.

3. **Analyze the Second Set: H2O, H2Te, H2Se, H2S**:
- H2O has strong hydrogen bonding, leading to a significantly higher boiling point compared to the others.
- H2Te, H2Se, and H2S will have boiling points determined by their molecular masses and Van der Waals forces.
- Order based on boiling points: H2O > H2Te > H2Se > H2S.

4. **Analyze the Third Set: Br2, Cl2, F2**:
- All are nonpolar molecules and exhibit dispersion forces (a type of Van der Waals force).
- The boiling points will increase with molecular mass: Br2 > Cl2 > F2.

5. **Analyze the Fourth Set: CH4, SiH4, GeH4**:
- CH4 does not have hydrogen bonding, while SiH4 and GeH4 are larger and have higher molecular masses.
- The order based on boiling points will be: GeH4 > SiH4 > CH4.

6. **Conclusion**:
- From the analysis, the correct order of decreasing boiling points for each set is:
- For HF, HI, HBr, HCl: **HF > HI > HBr > HCl**
- For H2O, H2Te, H2Se, H2S: **H2O > H2Te > H2Se > H2S**
- For Br2, Cl2, F2: **Br2 > Cl2 > F2**
- For CH4, SiH4, GeH4: **GeH4 > SiH4 > CH4**

### Final Answer:
The correct order of decreasing boiling points is:
1. HF > HI > HBr > HCl
2. H2O > H2Te > H2Se > H2S
3. Br2 > Cl2 > F2
4. GeH4 > SiH4 > CH4