The correct Lewis structure is: O=C=O (carbon in the center with double bonds to each oxygen; each O has two lone pairs; C has no lone pairs).
Explanation
- Total valence electrons: $4$ (C) + $6+6$ (two O) = $16$ electrons.
- Skeleton: O—C—O uses 2 bonds (4 e), leaving 12 e.
- Place lone pairs on oxygens to complete octets: after giving each O three lone pairs (6 e each) there are no electrons left but carbon has only 4 electrons (incomplete octet).
- Convert one lone pair from each O into bonding pairs to form double bonds: O=C=O. Now each O has two lone pairs and a double bond (octet satisfied), and C has four bonds (octet satisfied).
- Formal charges: each O: $6-(4+4/2)=0$; carbon: $4-(0+8/2)=0$. All formal charges are zero, so this is the best structure.
Geometry: linear, bond angle $180^\circ$.
(ASCII depiction)
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:O:: = C = ::O:
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