Which one of the following molecules does not have a dipole moment?

• A. H_2O
• B. CO_2
• C. NH_3
• D. SO_2

Answer: (B)

Verified step by step guidance

1. Recall that a molecule's dipole moment depends on both the polarity of its bonds and the geometry of the molecule, which determines how bond dipoles add up vectorially.
2. Analyze the molecular geometry and bond polarity of each molecule: H_2O has bent geometry with polar O-H bonds, NH_3 has trigonal pyramidal geometry with polar N-H bonds, SO_2 has bent geometry with polar S-O bonds, and CO_2 has linear geometry with polar C=O bonds.
3. Understand that in CO_2, the two polar C=O bonds are arranged linearly and symmetrically opposite each other, causing their dipole moments to cancel out, resulting in no net dipole moment.
4. In contrast, the bent or pyramidal shapes of H_2O, NH_3, and SO_2 cause their bond dipoles to add up to a net dipole moment, making these molecules polar.
5. Conclude that the molecule without a dipole moment among the options is CO_2 due to its linear geometry and symmetrical bond dipoles canceling each other.