LPG stands for liquefied petroleum gas.
It is a mixture of hydrocarbons which can be liquefied under pressure.
The major components of LPG are:
\[
\text{butane}
\]
and
\[
\text{isobutane}.
\]
In many cases, propane may also be present, but among the given options, the correct main constituents are butane and isobutane.
These gases burn easily and release a large amount of heat, so LPG is used as domestic fuel.
Therefore, LPG mainly contains:
\[
\text{Butane and Isobutane}.
\]