To determine which compounds among HF, NH3, H2S, and PH3 exhibit hydrogen bonding, we need to analyze the presence of hydrogen atoms bonded to highly electronegative atoms (such as nitrogen, oxygen, or fluorine) and the resulting dipole interactions.
### Step-by-Step Solution:
1. **Understanding Hydrogen Bonding**:
- Hydrogen bonding occurs when a hydrogen atom is covalently bonded to a highly electronegative atom (N, O, or F). This creates a partial positive charge on the hydrogen atom and a partial negative charge on the electronegative atom, allowing for attractive interactions between molecules.
2. **Analyzing HF (Hydrogen Fluoride)**:
- In HF, hydrogen is bonded to fluorine, which has a high electronegativity (4.0). This results in a significant partial positive charge on hydrogen and a partial negative charge on fluorine. Therefore, HF can form hydrogen bonds.
3. **Analyzing NH3 (Ammonia)**:
- In NH3, hydrogen is bonded to nitrogen, which has an electronegativity of 3.0. Similar to HF, this creates a partial positive charge on hydrogen and a partial negative charge on nitrogen, allowing NH3 to also form hydrogen bonds.
4. **Analyzing H2S (Hydrogen Sulfide)**:
- In H2S, hydrogen is bonded to sulfur, which has a lower electronegativity (2.5) compared to nitrogen and fluorine. The partial charges are not significant enough to allow for hydrogen bonding. Therefore, H2S does not exhibit hydrogen bonding.
5. **Analyzing PH3 (Phosphine)**:
- In PH3, hydrogen is bonded to phosphorus, which has an electronegativity of 2.1. Similar to H2S, the electronegativity difference is not sufficient to create significant partial charges, and thus PH3 cannot form hydrogen bonds.
6. **Conclusion**:
- The compounds that exhibit hydrogen bonding among the given options are HF and NH3.
### Final Answer:
The compounds showing hydrogen bonding are **HF and NH3**.
