The compound in which carbons uses only its sp hybrid orbitals for bond formation is

In Acetylene C2H2 carbons are 'sp' hybridization  In Propane C3H8,&Butane⁡C4H10 all carbons are sp3 hybridization In propyne  CH3↓3−C↓2≡C↓1Hsp3       sp     spC1sp,C2sp and C3sp3 hybridization