Addition reactions add across double bonds in unsaturated compounds

Steps:

• Recall addition reactions involve adding atoms or molecules across a carbon-carbon double bond in alkenes or unsaturated fats, without eliminating anything.
• Examine option A: Butane (saturated alkane) to ethene (alkene) and ethane involves breaking C-C bonds, a cracking reaction.
• Examine option B: Butane to ethane and hydrogen is dehydrogenation or cracking, removing hydrogen, not adding.
• Examine option C: Vegetable oils (unsaturated) to margarine adds hydrogen across double bonds via hydrogenation.
• Examine option D: Ethene with oxygen is combustion, an oxidation forming CO2 and H2O.

Why C is correct:

• Hydrogenation of vegetable oils adds H2 across C=C bonds, saturating the fats as in the reaction: R-CH=CH-R + H2 → R-CH2-CH2-R.

Why the others are wrong:

• A: Cracking decomposes alkanes into smaller hydrocarbons, not addition.
• B: Produces hydrogen from saturated butane, a removal reaction like dehydrogenation.
• D: Combustion oxidizes ethene completely: C2H4 + 3O2 → 2CO2 + 2H2O, not addition across a bond.

Final answer: C