Combustion breaks the C-C bond in ethane via oxidation.

Steps:

• Identify CH₃CH₃ as ethane (C₂H₆) with one C-C single bond.
• Examine combustion: ethane reacts with O₂ to form CO₂ and H₂O, cleaving the C-C bond.
• Review other options: hydrogenation, polymerization, and steam reaction do not break the C-C bond in ethane.
• Select the reaction that explicitly severs the C-C linkage.

Why A is correct:

• The combustion equation C₂H₆ + 7/2 O₂ → 2CO₂ + 3H₂O produces two CO₂ molecules, requiring C-C bond cleavage to separate the carbons.

Why the others are wrong:

• B: Hydrogenation adds H₂ across double bonds; ethane lacks unsaturation, so no reaction occurs and C-C remains intact.
• C: Polymerization joins unsaturated monomers; ethane cannot polymerize, preserving its C-C bond.
• D: Reaction with steam (reforming) for ethane requires high-temperature catalysis not implied here, so C-C bond is not broken under standard conditions.

Final answer: A