In which of the following compounds, H-bond exist?
I. HF
II. `NH_3`
III. `H_2O`
IV. HI
Select the correct option.

Options

A. I and II
B. III and IV
C. I, II and III
D. I, II and IV

Answer

To determine which of the given compounds exhibit hydrogen bonding, we need to analyze each compound based on the presence of highly electronegative atoms bonded to hydrogen. Hydrogen bonding typically occurs when hydrogen is covalently bonded to highly electronegative elements such as fluorine (F), oxygen (O), or nitrogen (N).

### Step-by-Step Solution:

1. **Identify the Compounds**: We have four compounds to analyze: HF, NH₃, H₂O, and HI.

2. **Check for Hydrogen Bonding in HF**:
- HF contains fluorine, which has a high electronegativity (4.0).
- Since HF has hydrogen bonded to fluorine, hydrogen bonding exists in HF.

3. **Check for Hydrogen Bonding in NH₃**:
- NH₃ contains nitrogen, which has a high electronegativity (3.0).
- Hydrogen is bonded to nitrogen, allowing for hydrogen bonding in NH₃.

4. **Check for Hydrogen Bonding in H₂O**:
- H₂O contains oxygen, which has a high electronegativity (3.5).
- Hydrogen is bonded to oxygen, so hydrogen bonding exists in H₂O.

5. **Check for Hydrogen Bonding in HI**:
- HI contains iodine, which has a lower electronegativity compared to F, O, and N.
- Since hydrogen is bonded to iodine, which is not sufficiently electronegative, hydrogen bonding does not occur in HI.

6. **Conclusion**:
- The compounds that exhibit hydrogen bonding are HF, NH₃, and H₂O.
- Therefore, the correct answer is I (HF), II (NH₃), and III (H₂O).

### Final Answer:
The correct options are I, II, and III.

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