Which of the following observations can be explained on the basis of hydrogen bonding ?
(i) H- F has higher boiling point than other halogen acids.
(ii) `H_(2)` O has highest boiling point among hydrides of group 16 elements.
(iii) `NH_(3)` has lower boiling point than `PH_(3)`.

Options

A. (i) , (ii) and (iii)
B. (i) and (iii)
C. (ii) and (iii)
D. (i) and (ii)

Explanation

To solve the question regarding which observations can be explained on the basis of hydrogen bonding, we will analyze each statement one by one.

### Step 1: Analyze Statement (i) - HF has a higher boiling point than other halogen acids.
- **Explanation**: Hydrogen fluoride (HF) exhibits hydrogen bonding due to the presence of a highly electronegative fluorine atom bonded to hydrogen. This results in strong intermolecular attractions between HF molecules, leading to a higher boiling point compared to other halogen acids like HCl, HBr, and HI, which do not exhibit hydrogen bonding due to the lower electronegativity of chlorine, bromine, and iodine.

### Step 2: Analyze Statement (ii) - H2O has the highest boiling point among hydrides of group 16 elements.
- **Explanation**: Water (H2O) has two hydrogen atoms bonded to a highly electronegative oxygen atom, allowing for significant hydrogen bonding. This strong intermolecular force results in a higher boiling point for water compared to other group 16 hydrides like H2S, H2Se, and H2Te, which do not form hydrogen bonds as effectively due to the lower electronegativity of sulfur, selenium, and tellurium.

### Step 3: Analyze Statement (iii) - NH3 has a lower boiling point than PH3.
- **Explanation**: Ammonia (NH3) exhibits hydrogen bonding due to the presence of nitrogen, which is electronegative. This leads to stronger intermolecular forces compared to phosphine (PH3), which does not form hydrogen bonds effectively. Therefore, ammonia has a higher boiling point than phosphine, making this statement incorrect.

### Conclusion:
Based on the analysis:
- Statement (i) is correct and can be explained by hydrogen bonding.
- Statement (ii) is correct and can be explained by hydrogen bonding.
- Statement (iii) is incorrect as NH3 has a higher boiling point than PH3 due to hydrogen bonding.

Thus, the observations that can be explained on the basis of hydrogen bonding are (i) and (ii).

### Final Answer:
The correct answer is: **(i) and (ii)**.

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