Ethene hydration as an addition reaction

Steps:

• Identify the reactants: ethene (C₂H₄) has a carbon-carbon double bond and reacts with steam (H₂O).
• Recall the product: ethanol (C₂H₅OH) forms by adding water across the double bond.
• Classify the reaction: the double bond breaks, and H and OH add to the carbons, characteristic of addition.
• Confirm type: no other reagents or conditions suggest alternative classifications.

Why A is correct:

• Addition reactions involve breaking a π-bond in alkenes and adding atoms/groups across it, as in C₂H₄ + H₂O → C₂H₅OH (catalyzed by acid).

Why the others are wrong:

• B: Fermentation produces ethanol from sugars via yeast enzymes, not from alkenes.
• C: Polymerisation links monomers like ethene into long chains, not forming small molecules like ethanol.
• D: Reduction adds hydrogen to decrease oxygen content, but here water adds without net H₂ gain.

Final answer: A