Besides fermentation, which of the following methods is now used to obtain large quantities of ethanol?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Hydration of ethene
Ethanol is obtained commercially by the fermentation of sugars, the oldest method, and nowadays in large quantities by the hydration of ethene. Water adds to the double bond in the presence of an acid as catalyst:
\( \displaystyle \ce{CH2=CH2 + H2O} \xrightarrow{\ce{H+}} \ce{CH3CH2OH} \)
Why the other options are incorrect
Option (2) Catalytic hydrogenation of carbon monoxide in the presence of ZnO–Cr2O3 — Incorrect. This is how most methanol is made today, at high pressure and temperature.
Option (3) Destructive distillation of wood — Incorrect. This was the old source of methanol, which is why methanol is called ‘wood spirit’.
Option (4) Reduction of ethanoic acid with lithium aluminium hydride — Incorrect. LiAlH4 does reduce carboxylic acids to primary alcohols, but it is an expensive reagent and is used only for preparing special chemicals, not for bulk ethanol.
NCERT (2026-27 edition):
7.5 Some Commercially Important Alcohols – “Ethanol, C2H5OH, is obtained commercially by fermentation, the oldest method is from sugars.” … “Nowadays, large quantities of ethanol are obtained by hydration of ethene (Section 7.4).”