Final answer:
Dipole-dipole forces exist between polar molecules such as CH₃Cl and HCl, which both have a net dipole moment, making option B) b and c the correct answer.
Step-by-step explanation:
The question asks which molecules have dipole-dipole forces. Dipole-dipole forces are intermolecular forces that exist between polar molecules with a permanent dipole moment. They occur when the positive end of one polar molecule is attracted to the negative end of another molecule.
Looking at the options given:
a. CBr₄ - Tetrahedral geometry with symmetric distribution of polar C-Br bonds, which results in no net dipole moment (nonpolar molecule).
b. CH₃Cl - This molecule is polar due to the difference in electronegativity between Cl and H atoms, causing a net dipole moment.
c. HCl - HCl is a classic example of a polar molecule with a significant dipole moment due to the difference in electronegativity between H and Cl atoms.
Therefore, the molecules that have dipole-dipole forces are b. CH₃Cl and c. HCl. The correct answer is B) b and c.