Hydrogen bonds may occur between:

• A. two hydrogen atoms in a nonpolar molecule
• B. two carbon atoms in a hydrocarbon chain
• C. a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom
• D. a hydrogen atom and a metal ion

Answer: (C)

Verified step by step guidance

1. Understand the concept of hydrogen bonding: Hydrogen bonds are weak interactions that occur when a hydrogen atom covalently bonded to an electronegative atom (like oxygen, nitrogen, or fluorine) is attracted to another electronegative atom.
2. Identify the key requirement for hydrogen bonding: The hydrogen atom must be covalently bonded to an electronegative atom, creating a partial positive charge on the hydrogen. This allows it to interact with another electronegative atom that has a partial negative charge.
3. Analyze the options provided: Eliminate options that do not involve an electronegative atom or do not meet the criteria for hydrogen bonding. For example, two hydrogen atoms in a nonpolar molecule or two carbon atoms in a hydrocarbon chain do not involve electronegative atoms and cannot form hydrogen bonds.
4. Focus on the correct scenario: A hydrogen atom covalently bonded to an electronegative atom (e.g., in water, where hydrogen is bonded to oxygen) can form a hydrogen bond with another electronegative atom (e.g., the oxygen of a neighboring water molecule).
5. Conclude that the correct answer is: 'a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom,' as this satisfies the conditions for hydrogen bonding.