In an alkyne, there is a carbon-carbon triple bond (C≡C). Carbon atoms involved in a triple bond adopt sp hybridization, which means each of the participating carbon atoms contributes one s-orbital and one p-orbital to form a hybrid sp orbital. The two sp orbitals on each carbon atom overlap end-to-end to create the σ (sigma) bond between them. The remaining unhybridized p-orbitals (two on each carbon atom) overlap sideways to form two π (pi) bonds, resulting in a triple bond.

Therefore, the hybridization of alkyne carbons involved in the triple bond is sp with a linear molecular geometry around each alkyne carbon.