### Correct Option: A. HF(g) #### Explanation of the Correct Answer: To understand why HF (hydrogen fluoride) has the strongest hydrogen bonds among the given options, we need to consider the concept of hydrogen bonding and the factors that influence its strength. 1. **Definition of Hydrogen Bonding**: - A hydrogen bond is a type of dipole-dipole interaction that occurs when a hydrogen atom covalently bonded to a highly electronegative atom (like fluorine, oxygen, or nitrogen) experiences an attraction to another electronegative atom. 2. **Electronegativity**: - Electronegativity is a measure of an atom's ability to attract and hold onto electrons. In the context of hydrogen bonding, the more electronegative the atom bonded to hydrogen, the stronger the hydrogen bond will be. - In the periodic table, electronegativity increases from left to right across a period and decreases from top to bottom within a group. 3. **Electronegativity Values**: - **Fluorine (F)**: 3.98 - **Nitrogen (N)**: 3.04 - **Chlorine (Cl)**: 3.16 - **Carbon (C)**: 2.55 - From these values, we can see that fluorine is the most electronegative element, followed by nitrogen, chlorine, and carbon. 4. **Analysis of Each Compound**: - **A. HF(g)**: In HF, the hydrogen atom is bonded to fluorine, which is highly electronegative. This creates a strong dipole, with a significant partial positive charge on hydrogen and a partial negative charge on fluorine. The strong attraction between these dipoles leads to very strong hydrogen bonds. - **B. NH3(g)**: In ammonia (NH3), hydrogen is bonded to nitrogen. While nitrogen is also electronegative, it is less so than fluorine. Therefore, the hydrogen bonds in NH3 are strong but not as strong as those in HF. - **C. CH4(g)**: In methane (CH4), hydrogen is bonded to carbon, which is much less electronegative than nitrogen or fluorine. As a result, there are no significant hydrogen bonds in CH4; it primarily exhibits weak van der Waals forces. - **D. HCl(g)**: In hydrogen chloride (HCl), hydrogen is bonded to chlorine. Chlorine is more electronegative than hydrogen, but less so than nitrogen and fluorine. The hydrogen bonds in HCl are weaker than those in HF and NH3. 5. **Conclusion**: - Since HF has the strongest electronegative atom (fluorine) bonded to hydrogen, it forms the strongest hydrogen bonds compared to NH3, CH4, and HCl. Therefore, HF(g) is the correct answer. #### Why Other Options Are Weaker: - **B. NH3(g)**: While NH3 does form hydrogen bonds, they are not as strong as those in HF due to nitrogen's lower electronegativity compared to fluorine. - **C. CH4(g)**: Methane does not form hydrogen bonds at all because carbon is not electronegative enough to create a significant dipole with hydrogen. The interactions in CH4 are primarily weak van der Waals forces. - **D. HCl(g)**: Hydrogen chloride does form hydrogen bonds, but they are weaker than those in HF and NH3 due to chlorine's lower electronegativity compared to fluorine. ### Revision Summary: - Hydrogen bonds are strongest when hydrogen is bonded to highly electronegative atoms (F, O, N). - HF has the strongest hydrogen bonds due to fluorine's high electronegativity. - NH3 has strong hydrogen bonds but weaker than HF due to nitrogen's lower electronegativity. - CH4 does not form hydrogen bonds, and HCl has weaker hydrogen bonds than HF and NH3.