Concept: Hydrogen Bonding

Hydrogen bonding is a special type of dipole-dipole interaction that occurs when hydrogen is bonded to a highly electronegative atom (typically F, O, or N). The hydrogen atom, being partially positive, is then attracted to a lone pair of electrons on another highly electronegative atom in an adjacent molecule or within the same molecule.

Why (C) is correct:

In ${\mathrm{N}}_2{\mathrm{H}}_4$ (hydrazine), hydrogen atoms are directly bonded to nitrogen atoms. Nitrogen is a highly electronegative atom, and it also possesses a lone pair of electrons. This allows for the formation of intermolecular hydrogen bonds between ${\mathrm{N}}_2{\mathrm{H}}_4$ molecules.

Option Analysis:

• A) ${\mathrm{CH}}_4$ (Methane): Carbon is not sufficiently electronegative to form hydrogen bonds.
• B) ${\mathrm{H}}_2\mathrm{Se}$ (Hydrogen Selenide): Selenium is not sufficiently electronegative to form hydrogen bonds.
• D) ${\mathrm{H}}_2\mathrm{S}$ (Hydrogen Sulfide): Sulfur is not sufficiently electronegative to form hydrogen bonds.

Correct Answer: (C)