The gas which is used to make chloroform is

The correct option is Methane.

Chloroform, chemically known as trichloromethane (${\mathrm{CHCl}}_3$), is industrially produced by heating a mixture of methane (${\mathrm{CH}}_4$) and chlorine. This reaction is a free-radical halogenation process that occurs in the presence of ultraviolet (UV) light or heat.

During the chlorination of methane, hydrogen atoms in the methane molecule are successively replaced by chlorine atoms through a series of substitution steps:
1. Methane reacts with chlorine to form chloromethane:
${\mathrm{CH}}_4+{\mathrm{Cl}}_2\to {\mathrm{CH}}_3\mathrm{Cl}+\mathrm{HCl}$
2. Chloromethane reacts with more chlorine to form dichloromethane:
${\mathrm{CH}}_3\mathrm{Cl}+{\mathrm{Cl}}_2\to {\mathrm{CH}}_2{\mathrm{Cl}}_2+\mathrm{HCl}$
3. Dichloromethane reacts further with chlorine to produce chloroform (trichloromethane):
${\mathrm{CH}}_2{\mathrm{Cl}}_2+{\mathrm{Cl}}_2\to {\mathrm{CHCl}}_3+\mathrm{HCl}$

Therefore, methane is the key starting gas utilized to manufacture chloroform.