Which among the following compounds is the main constituent of natural gas ?

Question

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Correct — B, Methane. Natural gas as it comes out of a well is a mixture of gaseous hydrocarbons in which methane, CH4, is overwhelmingly dominant — commonly around ninety-five per cent of processed pipeline gas. The remainder is a small tail of heavier alkanes (ethane, propane, butane) together with carbon dioxide, nitrogen, sometimes hydrogen sulphide, and traces of helium, all of which are stripped out to varying degrees at the processing plant. Methane's dominance is why the whole downstream vocabulary works the way it does: compressed natural gas is nothing more than this same gas squeezed to two hundred bar or more, so CNG is also essentially methane; liquefied natural gas is the same gas cooled to about minus 162 degrees Celsius; and piped natural gas delivered to homes is again methane. It is also why natural gas is the cleanest of the fossil fuels per unit of energy — methane has the highest hydrogen-to-carbon ratio of any hydrocarbon, so more of its energy comes from making water and less from making carbon dioxide.

Why the other options are wrong — (a) Hexane, C6H14, is a liquid at ordinary temperature and pressure, so it cannot be the main constituent of a gas. It belongs to the light-naphtha fraction of crude oil and is used industrially as a solvent, notably for extracting edible oil from oilseeds — not as a component of the gas stream.  (c) This is the intended trap, because butane is a real natural-gas component — but only a minor one. Butane, with propane, is the main constituent of LPG, the cooking-gas cylinder, which is a refinery and gas-processing product recovered from the heavier fraction. Keep the two apart: natural gas and CNG are methane; LPG is propane and butane. UPPSC asked exactly this contrast in 2021, where the main constituent of LPG was the answer.  (d) Benzene, C6H6, is an aromatic hydrocarbon, not an alkane, and it is a liquid at room temperature. It is a product of petroleum refining and coal carbonisation and a recognised carcinogen; it is not a constituent of natural gas.

Concept: Fossil fuel gases are distinguished by which hydrocarbons dominate them, and each has its own name and use. Natural gas, and therefore CNG, LNG and PNG, is mainly methane. LPG is mainly propane and butane, liquefied under modest pressure. Biogas from anaerobic digestion is roughly two-thirds methane and one-third carbon dioxide. Coal gas is a manufactured mixture of hydrogen, methane and carbon monoxide, and water gas is carbon monoxide with hydrogen. The physical differences follow from the chemistry: methane is lighter than air, so a CNG leak rises and disperses, whereas propane and butane are heavier than air and a leaking LPG cylinder pools at floor level — the single most important safety contrast between the two.

State PCS 2022 Q92 — Science & Technology PYQ with Answer

State PCS 2022 Q92 — Science & Technology PYQ with Answer