Answer: is mostly methane
Step-by-step explanation:
Natural gas is the naturally generating mixture which is composed of methane as primary component and other alkane elements .It is also described as fossil fuel from the nature. Natural gas is hydrocarbon that is utilized while cooking, fuel for vehicles, heating etc.
Other options are incorrect because natural gas is non-renewable resource , carbon dioxide and water gets created after burning natural gas and is not responsible for generating electricity in amount of 75%.