Ethene hydration via electrophilic addition

Steps:

• Identify reactants: Ethene (C₂H₄) reacts with water (H₂O) to form ethanol (C₂H₅OH).
• Recognize reaction type: The C=C double bond in ethene breaks, adding H⁺ and OH⁻ across it.
• Confirm mechanism: Acid-catalyzed hydration follows Markovnikov's rule for alkene addition.
• Eliminate alternatives: Other processes do not match the transformation.

Why A is correct:

• Addition reactions involve breaking a π-bond in alkenes to attach new atoms, as in the formula C₂H₄ + H₂O → C₂H₅OH (with H₂SO₄ catalyst).

Why the others are wrong:

• B: Combustion oxidizes hydrocarbons with O₂ to produce CO₂ and H₂O, not ethanol.
• C: Polymerisation joins ethene monomers into long chains like polyethene, not a single alcohol molecule.
• D: Substitution replaces one atom/group in saturated compounds, but ethene's double bond requires addition.

Final answer: A