Read the passage carefully and answer the Questions.
Alcohols and phenols are obtained when a hydrogen atom in aliphatic and aromatic hydrocarbons respectively, is replaced by - OH group. These compounds find wide applications in industry as well as in our daily life. You may notice that ordinary spirit is used for polishing wooden furniture which is chiefly a compound containing hydroxyl group. An alcohol contains one or more hydroxyl (OH) group(s) directly attached to carbon atom(s), of an aliphatic system (\( CH_3OH \)) while a phenol contains -OH group(s) directly attached to carbon atom(s) of an aromatic system (\( C_6H_5OH \)). Alcohols are prepared by the hydration of alkenes, fermentation of glucose, and reduction of carbonyl compounds. Alcohols produce alkenes upon dehydration whereas alkenes on acid catalyzed hydration convert into alcohols.
An alkyl halide can be converted into alcohol through
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → substitution
In an alkyl halide the C–X bond is polar: the carbon carries a partial positive charge. A nucleophile such as \( \ce{OH-} \) attacks this carbon and pushes out the halide ion. One group is replaced by another, so this is a nucleophilic substitution reaction. Boiling an alkyl halide with aqueous KOH (or moist silver oxide) converts it into an alcohol:
\( \displaystyle \ce{R-X + KOH} \xrightarrow{\text{aqueous}} \ce{R-OH + KX} \)
\( \displaystyle \ce{CH3CH2Br + KOH} \xrightarrow{\text{aqueous}} \ce{CH3CH2OH + KBr} \)
So an alkyl halide is converted into an alcohol through substitution.
Why the other options are incorrect
Option (1) addition — Incorrect. Addition takes place across a multiple bond, as when water adds to an alkene in acid-catalysed hydration; an alkyl halide has no multiple bond to add to.
Option (2) elimination — Incorrect. Elimination removes atoms from neighbouring carbons and forms a double bond, so it gives an alkene, not an alcohol.
Option (4) dehydrohalogenation — Incorrect. This is the elimination of HX from an alkyl halide by alcoholic KOH: \( \ce{CH3CH2Br + KOH -> CH2=CH2 + KBr + H2O} \). The product is again an alkene.
NCERT (2026-27 edition):
Nucleophilic Substitution Reactions
Table 6.4: Nucleophilic Substitution of Alkyl Halides (R–X) (row)
| Reagent | Nucleophile (Nu–) | Substitution product R–Nu | Class of main product |
|---|---|---|---|
| NaOH (KOH) | HO– | ROH | Alcohol |