What forms a hydrogen bond?

Hydrogen bonds form through the attraction between a hydrogen atom that is covalently bonded to a highly electronegative atom (like oxygen or nitrogen) and another electronegative atom. In this context, when hydrogen, which possesses a partial positive charge due to its covalent bond with an electronegative atom, is attracted to the lone pair of electrons of another electronegative atom in a different molecule, a hydrogen bond is established. This process is crucial in many biological processes, such as the formation of water’s unique properties and the structure of proteins and nucleic acids.

The other options do not accurately describe the formation of hydrogen bonds. Migrating electrons to the nucleus does not relate to bond formation between molecules. Equal sharing of electrons characterizes covalent bonds rather than hydrogen bonds. A strong bond between hydrogen and oxygen typically refers to a covalent bond, which differs fundamentally from the relatively weaker interactions of hydrogen bonds.