Read the passage carefully and answer the questions.
Replacement of a hydrogen atom in a hydrocarbon by an alkoxy or carboxyl group yields a class of compounds known as ethers. Ethers are classified as symmetrical or unsymmetrical on the basis of groups attached to the oxygen atoms. Diethyl ether, a symmetrical ether, has been widely used as an inhalation anesthetic. Ethers can be prepared by acid catalyzed intermolecular dehydration of alcohols and Williamson's synthesis. Acid catalyzed dehydration of alcohols is not generally preferred as it gives a mixture of elimination and substitution products. In Williamson's synthesis, an alkyl halide is allowed to react with sodium alkoxide. Ethers containing substituted Alkyl groups may also be prepared by this method. The C-O bond in ether is weakly polar and is cleaved under drastic conditions with excess of hydrogen halides. In electrophilic substitution, the alkoxy group deactivates the aromatic ring and directs the incoming group to ortho and para positions.
When ethanol is dehydrated in the presence of \( H_2SO_4 \) at 443 K and 413 K respectively the products formed are
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Ethene and ethoxyethane
Alcohols lose water when heated with a protic acid such as concentrated sulphuric acid, and the temperature decides the product. At the higher temperature one molecule of ethanol loses water internally, giving an alkene (intramolecular dehydration). At the lower temperature, with ethanol in excess, two molecules lose one molecule of water between them, giving an ether (intermolecular dehydration).
At 443 K:
\( \displaystyle \ce{C2H5OH} \xrightarrow[\text{443 K}]{\text{conc. }\ce{H2SO4}} \ce{CH2=CH2 + H2O} \)
At 413 K:
\( \displaystyle \ce{2C2H5OH} \xrightarrow[\text{413 K}]{\text{conc. }\ce{H2SO4}} \ce{C2H5-O-C2H5 + H2O} \)
So the products at 443 K and 413 K are ethene and ethoxyethane, respectively.
Why the other options are incorrect
Option (1) Ethane and ethoxyethane — Incorrect. Dehydration removes water and creates a double bond; ethane would need the addition of hydrogen.
Option (2) Ethylmethyl ether and butene — Incorrect. Two ethyl groups give diethyl ether, not ethyl methyl ether, and a two-carbon alcohol cannot give butene.
Option (3) Ethylmethyl ether and propene — Incorrect. Neither product has the carbon skeleton of ethanol; dehydration does not add or remove carbon atoms.
Note: It seems that there is a mistake in the original NTA paper, which prints alkoxy or carboxyl group when it should read alkoxy or aryloxy group, and deactivates when it should read activates.
NCERT (2026-27 edition):
By Dehydration of Alcohols
