\((A)\) will be:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → diethyl ether, CH3–CH2–O–CH2–CH3
Alcohols are dehydrated by protic acids such as concentrated \( \ce{H2SO4} \), and the temperature decides the product: ethanol gives ethene at 443 K but ethoxyethane (diethyl ether) at 413 K. At the lower temperature a protonated ethanol molecule is attacked by a second ethanol molecule (SN2), which removes water between two molecules:
\( \displaystyle \ce{C2H5OH + H+ -> C2H5OH2+} \)
\( \displaystyle \ce{C2H5OH + C2H5OH2+ -> C2H5-O^+(H)-C2H5 + H2O} \)
\( \displaystyle \ce{C2H5-O^+(H)-C2H5 -> C2H5OC2H5 + H+} \)
The net reaction is:
\( \displaystyle \ce{2C2H5OH} \xrightarrow{\ce{H2SO4},\ \text{413 K}} \ce{C2H5OC2H5 + H2O} \)
So (A) is diethyl ether.
Why the other options are incorrect
Option (1) ethene, H2C=CH2 — Incorrect. Formed when the same mixture is heated to the higher temperature of 443 K (intramolecular dehydration).
Option (2) ethyne, HC≡CH — Incorrect. Removing water from ethanol cannot create a triple bond; ethyne is made from \( \ce{CaC2} \) and water.
Option (4) ethane-1,2-diol, HO–CH2–CH2–OH — Incorrect. A diol is formed by oxidation of ethene (e.g. cold alkaline \( \ce{KMnO4} \)), not by dehydration of ethanol.
NCERT (2026-27 edition):
By Dehydration of Alcohols – “Alcohols undergo dehydration in the presence of protic acids (H2SO4, H3PO4). The formation of the reaction product, alkene or ether depends on the reaction conditions. For example, ethanol is dehydrated to ethene in the presence of sulphuric acid at 443 K. At 413 K, ethoxyethane is the main product.”