Which of the following would most likely be a gas at room temperature? Justify your choice. (a) \(\mathrm{NaCl}\) (b) \(\mathrm{C}_{2} \mathrm{H}_{2}\) (c) Na metal (d) \(\mathrm{CH}_{3} \mathrm{~F}\)

(a) \(\mathrm{NaCl}\): Ionic bonding - very strong electrostatic attraction between positively charged metal cations (Na+) and negatively charged nonmetal anions (Cl-). (b) \(\mathrm{C}_{2} \mathrm{H}_{2}\): Covalent bonding - consists of carbon-hydrogen bonds, primarily experiencing Vander Waals dispersion forces which are very weak. (c) Na metal: Metallic bonding - consists of a sea of delocalized electrons surrounding closely packed metal cations. (d) \(\mathrm{CH}_{3} \mathrm{~F}\): Covalent bonding - consists of carbon-hydrogen and carbon-fluorine bonds, experiencing Vander Waals dispersion forces as well as dipole-dipole interactions due to the polar nature of the carbon-fluorine bond.

(a) \(\mathrm{NaCl}\): Ionic bonding is very strong, resulting in a high melting and boiling point. This substance is unlikely to be a gas at room temperature. (b) \(\mathrm{C}_{2} \mathrm{H}_{2}\): Vander Waals dispersion forces are very weak, which often result in low melting and boiling points. This substance has a high possibility of being a gas at room temperature. (c) Na metal: Metallic bonding is strong and results in high melting and boiling points for metals. This substance is unlikely to be a gas at room temperature. (d) \(\mathrm{CH}_{3} \mathrm{~F}\): The presence of dipole-dipole interactions due to the polar nature of the carbon-fluorine bond makes the intermolecular forces stronger than in \(\mathrm{C}_{2} \mathrm{H}_{2}\). However, these forces are still weaker compared to ionic or metallic bonding. This substance could be a gas at room temperature, but less likely than \(\mathrm{C}_{2} \mathrm{H}_{2}\).

Considering the type of bonding and the intermolecular forces present in each of the given substances, \(\mathrm{C}_{2} \mathrm{H}_{2}\), with its weak Vander Waals dispersion forces, is the most likely substance to be a gas at room temperature.