Why Correct: Commercial LPG cylinders contain a mixture of butane and propane gases, with ratios adjusted seasonally.
Distractor Analysis: Isobutane is a structural isomer of butane used in some industrial applications but not standard LPG. Butane, isobutane and propane together describes various hydrocarbon mixtures but not typical LPG composition.
Takeaway: LPG composition varies by climate: winter blends contain more propane (higher vapor pressure at low temperatures), summer blends contain more butane.

Why Correct: Biogas comprises 50-75% methane, 25-50% carbon dioxide, and trace gases like hydrogen sulfide, nitrogen, and hydrogen.
Distractor Analysis: Carbon monoxide is toxic and absent in typical biogas. Ethane appears in natural gas but not in biogas. Hydrogen occurs only in trace amounts, not as a major component.
Takeaway: Anaerobic digestion of organic waste like manure, crop residues, or sewage produces biogas, a renewable energy source.

Why Correct: Coal, petroleum, and natural gas are fossil fuels formed from the decomposition of ancient organic matter under heat and pressure over millions of years.
Distractor Analysis: Cryogenic fuels are extremely cold liquefied gases like liquid hydrogen used in rockets. Indigenous fuels refer to locally available energy sources, which could include fossil fuels but is not their defining category. Radioactive fuels undergo nuclear fission, like uranium and plutonium in nuclear reactors.
Takeaway: Fossil fuels are non-renewable and their combustion releases greenhouse gases, primarily carbon dioxide, contributing to global warming.