Answer:
sp
Step-by-step explanation:
Hybridization is the combination of atomic orbitals to yield equivalent hybrid orbitals of appropriate energy which can participate in bonding.
In every compound there is a central atom. The central atom is usually the least electronegative atom in the molecule. In this case the least electronegative atom in the molecule is carbon.
The bond between carbon and oxygen in CO2 is intermittent between a pure double and a pure triple bond. Hence, carbon is sp hybridized.