The suitable reagents used for the following conversion is

$CH_3CH_2CH_2CH_3→CH_3CH_2CH_2CH_2Cl + CH_3CH_2CHClCH_3$

$Cl_2$/UV light

The correct answer is Option (1) → $Cl_2$/UV light

Complete statement:

The conversion of butane $(CH_3CH_2CH_2CH_3)$ into a mixture of 1-chlorobutane and 2-chlorobutane occurs by free radical chlorination in the presence of chlorine and ultraviolet (UV) light.

Reasoning:

• $Cl_2$ / UV light - Correct. UV light breaks Cl2 into free radicals, starting a substitution reaction. This produces both primary and secondary alkyl chlorides, hence a mixture of products.

• $NaCl + H_2SO_4$ - Incorrect. This combination is used to produce HCl gas, not for chlorinating alkanes.

• $Cl_2$ gas in the dark - Incorrect. Without light or heat, free radicals are not formed, so the reaction does not proceed.

• $Cl_2$ with iron in the dark - Incorrect. Iron acts as a catalyst mainly for aromatic chlorination, not for alkane free-radical substitution.

Hence, the suitable reagent is chlorine in the presence of UV light.