The carbon atom is SP hybridized while the oxygen atom is SP2 hybrized.
What are resonance structures?
The term resonance structures are those structures that can be used to explain the bonding in a molecule. Sometimes, a single structure is insufficient in explaining the structure of a compound.
Now looking at the two sturctures, Z is better because there are mo formal charges which make the molecle less stable unlike in X. In the CO2 molecule, the carbon atom is SP hybridized while the oxygen atom is SP2 hybrized.
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