The suitable reagents used for the following conversion is
\( CH_3CH_2CH_2CH_3→CH_3CH_2CH_2CH_2Cl + CH_3CH_2CHClCH_3 \)
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \(Cl_2\)/UV light
The reaction replaces a hydrogen atom of an alkane by chlorine. Alkanes have only strong, non-polar C–H and C–C bonds, so they do not react with ionic or polar reagents; they react by a free radical chain mechanism, which needs UV light or heat to split the chlorine molecule into atoms:
\( \displaystyle \ce{Cl2} \xrightarrow{h\nu} 2\,\mathrm{Cl}^{\bullet} \)
\( \displaystyle \ce{CH3CH2CH2CH3} + \mathrm{Cl}^{\bullet} \rightarrow \mathrm{C_{4}H_{9}}^{\bullet} + \ce{HCl} \)
\( \displaystyle \mathrm{C_{4}H_{9}}^{\bullet} + \ce{Cl2} \rightarrow \ce{C4H9Cl} + \mathrm{Cl}^{\bullet} \)
The chlorine atom can remove a hydrogen atom from an end carbon (primary H) or from a middle carbon (secondary H), so a mixture of isomers is formed, 1-chlorobutane and 2-chlorobutane, the very products shown:
\( \displaystyle \ce{CH3CH2CH2CH3} \xrightarrow{\ce{Cl2}/\text{UV light}} \ce{CH3CH2CH2CH2Cl + CH3CH2CHClCH3} \)
Why the other options are incorrect
Option (2) \(NaCl +H_2SO_4\) — Incorrect. This mixture produces HCl gas. HCl converts alcohols into alkyl chlorides, but it does not substitute the hydrogen of an alkane.
Option (3) \(Cl_2\) gas in the dark — Incorrect. In the dark, at room temperature, no chlorine atoms are formed to start the chain, so the alkane does not react.
Option (4) \(Cl_2\) gas in the presence of iron in the dark — Incorrect. Iron forms \( \ce{FeCl3} \), a Lewis acid that produces \( \ce{Cl+} \) for electrophilic substitution of arenes (benzene gives chlorobenzene); an alkane has no π electrons to attack.
NCERT (2026-27 edition):
From Alkanes by Free Radical Halogenation
