In a Lewis structure for CO2, which describes the formal charges and resonance forms?

• A. Formal charges on all atoms are zero; two equivalent resonance forms with double bonds.
• B. Carbon has +1; O -1
• C. Carbon 0; O -3
• D. All are -1

Answer: (A)

In CO2, the key idea is how formal charges and resonance forms describe electron distribution in a stable Lewis structure. Each oxygen forms a double bond to carbon, and carbon also forms two double bonds, with no lone pairs on carbon and two lone pairs on each oxygen. When you calculate formal charges using FC = V − NNonbonding − 1/2 Nbonds, you get zero for every atom: carbon has 4 valence minus 0 nonbonding minus 1/2 of 8 bonding electrons, which is 0; each oxygen has 6 valence minus 4 nonbonding minus 1/2 of 4 bonding electrons, which is also 0. Since the molecule has no net charge, these zero formal charges are consistent.

There are two equivalent resonance forms because you can shift which C=O bond is double, but both forms are identical in terms of formal charges — zero on all atoms. That’s why the best description is that all atoms carry zero formal charge and the molecule has two equivalent resonance forms with double bonds.

The other possibilities would require nonzero formal charges that don’t sum to the molecule’s overall zero charge, which doesn’t fit CO2’s actual electron bookkeeping.