The hybridization of C2H2 is sp. This is because each carbon atom in C2H2 has two bonds to hydrogen atoms and one bond to the other carbon atom. The two bonds to hydrogen atoms are sigma bonds, and the bond between the two carbon atoms is a pi bond. The sp hybridization of the carbon atoms results in the formation of two p orbitals that are perpendicular to each other. These p orbitals overlap to form the pi bond between the two carbon atoms.