Final answer:
Acetylene has the shortest C-H bond because it has a triple bond between the carbon atoms, indicating sp-hybridization, which leads to a shorter and stronger C-H bond due to more s-character.
Step-by-step explanation:
The student asked which compound has the shortest C-H bond among acetylene, cyclobutane, benzene, ethane, and ethylene. Bonds in organic molecules can vary in length, with stronger, shorter bonds typically found in molecules with greater s-character in their hybridized orbital structure. Acetylene has a C-H bond which is part of a C-C triple bond structure, indicative of sp-hybridisation, which has more s-character and hence shorter and stronger C-H bonds. Cyclobutane, benzene, and ethane have sp3 and sp2 hybridized carbons respectively, and while ethylene has sp2 hybridization, the presence of a double bond only, assigning acetylene with the shortest C-H bond.