Ethanol is obtained commercially by:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Fermentation
Ethanol is made commercially by fermentation: yeast acts on a sugary material, usually molasses left over from sugar mills (or starch from grains), and its enzymes break the sugar down into ethanol and carbon dioxide, \(\ce{C6H12O6 -> 2C2H5OH + 2CO2}\). The ethanol is then separated from the fermented liquid by distillation.
Why the other options are incorrect
Option (1) Dehydration — Incorrect. Dehydration removes water; heating ethanol with concentrated sulphuric acid dehydrates it to ethene, so it uses up ethanol.
Option (2) Distillation — Incorrect. Distillation only separates and concentrates the ethanol that fermentation has already made.
Option (4) Evaporation — Incorrect. Evaporation only turns a liquid into vapour; it makes no new substance.