Which of the following molecules has the smallest dipole-dipole forces?

• A. SO2
• B. HCl
• C. CO
• D. CH4

Answer: (D)

Verified step by step guidance

1. Step 1: Understand that dipole-dipole forces occur between polar molecules, which have a permanent dipole moment due to differences in electronegativity and molecular geometry.
2. Step 2: Analyze each molecule's polarity by considering both the electronegativity differences between atoms and the molecular shape to determine if the molecule is polar or nonpolar.
3. Step 3: For SO\_2, note that it has a bent shape and polar S=O bonds, resulting in a net dipole moment, so it is polar with significant dipole-dipole forces.
4. Step 4: For HCl, recognize it is a diatomic molecule with a large electronegativity difference between H and Cl, making it polar and thus having dipole-dipole forces.
5. Step 5: For CO, although it is a diatomic molecule, it has a small dipole moment due to the difference in electronegativity between C and O, so it has dipole-dipole forces but weaker than HCl and SO\_2; CH\_4, however, is nonpolar due to its symmetrical tetrahedral shape and identical C-H bonds, so it has the smallest dipole-dipole forces (essentially none).