OPSC OAS 2020 PrelimsScience & TechnologyQuestion 9
Solved previous year question from the OPSC OAS/OCS 2020 Preliminary Examination (General Studies), with the official answer key and a detailed explanation.
Question
The main component of biogas is:
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Answer & Explanation
Correct answer: (C) Methane
- Methane (CH₄) is the main component of biogas, constituting approximately 50-75% of the total biogas composition.
- Biogas is produced by the anaerobic decomposition (decomposition in the absence of oxygen) of organic matter such as animal dung, plant waste, sewage, and agricultural residues by methanogenic bacteria.
Composition of Biogas
| Component | Chemical Formula | Percentage |
|---|---|---|
| Methane | CH₄ | 50–75% (main component) |
| Carbon Dioxide | CO₂ | 25–50% |
| Hydrogen Sulphide | H₂S | 0–3% (trace amount, gives foul smell) |
| Nitrogen | N₂ | 0–10% |
| Hydrogen | H₂ | 0–1% |
| Water Vapour | H₂O | Variable |
The other options are incorrect
| Option | Details |
|---|---|
| (A) Butane (C₄H₁₀) | Component of Liquefied Petroleum Gas (LPG), not the main component of biogas |
| (B) Ethylene (C₂H₄) | A plant hormone and industrial chemical, not a component of biogas |
| (D) Propane (C₃H₈) | Component of LPG and natural gas, not the main component of biogas |
