Ethanol reacts with concentrated tetraoxosulphate(VI) acid at a temperature above 170°C to form

Correct answer: ethene.

Explanation: Concentrated H₂SO₄ at temperatures above about 170 °C dehydrates ethanol, eliminating water to form an alkene:

\(\text{C}_2\text{H}_5\text{OH} \;\xrightarrow[\;>170^\circ\text{C}\;]{\text{conc. } \text{H}_2\text{SO}_4}\; \text{C}_2\text{H}_4 + \text{H}_2\text{O}\)

• ethanone — Not formed from dehydration of ethanol.
• ethyne — A triple-bond product; not obtained by simple dehydration of ethanol.
• ethanal — Aldehyde; would come from oxidation of ethanol, not dehydration.