Final answer:
The molecule with the smallest dipole-dipole forces among CH₃Cl, HBr, O₂, and NO is O₂ since it is a nonpolar molecule with equal sharing of electrons and therefore no permanent dipole. The correct option is (C)
Step-by-step explanation:
The student's question pertains to the identification of the molecule with the smallest dipole-dipole forces among the options provided: CH₃Cl, HBr, O₂, and NO. Dipole-dipole forces are a type of intermolecular force that occur between polar molecules, where there is an uneven distribution of electrons.
When we assess the given molecules, we need to consider their polarity. Molecules CH₃Cl and HBr are polar because of the differences in electronegativity between the bonded atoms, hence they exhibit dipole-dipole forces. In contrast, O₂ is a homonuclear diatomic molecule with no difference in electronegativity between the atoms, leading to no permanent dipole and therefore no dipole-dipole forces. NO is weakly polar due to the small difference in electronegativity between nitrogen and oxygen, but it generally has weaker dipole moments than CH₃Cl and HBr.
To answer the student's question, O₂, being a nonpolar molecule, would have the smallest (actually null) dipole-dipole forces amongst the options listed.