Final answer:
Acetylene (C2H2) is hydrogenated to form ethane (C2H6). Acetylene's triple bond is broken and additional hydrogens are added to each carbon, resulting in ethane, not butane which has four carbon atoms.
Step-by-step explanation:
Acetylene is hydrogenated to form ethane (C2H6). When acetylene (C2H2) undergoes a hydrogenation reaction, each of the carbon atoms bonds to an additional hydrogen atom, thereby breaking the triple bond and forming a single bond between the carbons. The resulting molecule is ethane, which is an alkane with two carbon atoms, each bonded to three hydrogen atoms, forming a stable molecule. This is in contrast to butane (C4H10), which has four carbon atoms and would not be the direct product of acetylene hydrogenation.