Which one of the following statements is NOT correct?
- (a)Biomass is a renewable source of energy
- (b)Gobar gas is produced when cow-dung, crop residues, vegetable waste and sewage are allowed to decompose in the absence of oxygen
- (c)Biogas generation reduces soil and water pollution
- (d)Heating capacity of biogas is very low
Correct — D, 'Heating capacity of biogas is very low'. This is the statement that is NOT correct. Biogas is roughly 55-70% methane, which gives it a good calorific value and makes it an effective cooking and heating fuel — so calling its heating capacity 'very low' is wrong. The other three statements are all true.
- (a)Biomass is a renewable source of energy — This statement is correct — biomass (plant and animal matter) regrows and is classed as a renewable energy source, so it is not the wrong statement being sought.
- (b)Gobar gas is produced when cow-dung, crop residues, vegetable waste and sewage are allowed to decompose in the absence of oxygen — This statement is correct — gobar (bio)gas is produced by anaerobic decomposition (in the absence of oxygen) of such organic wastes, so it is a true statement, not the answer.
- (c)Biogas generation reduces soil and water pollution — This statement is correct — using organic waste for biogas and returning the digested slurry as manure reduces pollution, so it is true and not the wrong statement.
Biogas (gobar gas) is produced by anaerobic digestion of organic matter such as cattle dung, crop residues and sewage. The gas is mainly methane with carbon dioxide, giving it a useful calorific value as a clean cooking and lighting fuel, while the leftover slurry serves as nutrient-rich manure.
This is a 'pick the false statement' item. Three statements praise biogas/biomass and are true; the odd one claims biogas has 'very low' heating capacity, which contradicts its methane-rich, good-calorific-value nature.
- Biogas is about 55-70% methane, the rest mostly carbon dioxide.
- It is produced by anaerobic (oxygen-free) decomposition of organic waste.
- Its methane content gives it a good calorific value as a fuel.
- The residual slurry is used as manure, and biomass is a renewable energy source.
- Reading the question as 'which is correct' and picking a true statement.
- Believing biogas is a weak fuel — its methane content gives it a good heating value.
Asked as 'which statement is NOT correct' — scan for the one claim that contradicts the others.
Match List I (Fuel Gases) with List II (Major Constituents): (A) CNG (B) Coal gas (C) LPG (D) Water gas; 1. Carbon monoxide, Hydrogen 2. Butane, Propane 3. Methane, Ethane 4. Hydrogen, Methane, Carbon monoxide.
- (a) A 2 B 1 C 3 D 4
- (b) A 3 B 4 C 2 D 1
- (c) A 2 B 4 C 3 D 1
- (d) A 3 B 1 C 2 D 4
Answer(b) A 3 B 4 C 2 D 1
Same theme — fuel gases and their constituents. UPSC 2004 matches gases to their major components (methane-rich fuels); this NDA item tests the properties of biogas, which is likewise methane-rich.
Which one of the following is the major constituent of biogas?
- (a) Carbon dioxide
- (b) Nitrous oxide
- (c) Methane
- (d) Oxygen
Answer(c) Methane
Same fuel — biogas. That NDA item names its major constituent (methane); this one tests statements about biogas, including the false claim that its heating capacity is very low.
- practice — not a real PYQ
The major combustible constituent of biogas is
- (a)Carbon dioxide
- (b)Methane
- (c)Hydrogen
- (d)Nitrogen
Answer(b) Methane — it makes up the bulk of biogas and gives it its calorific value.
- practice — not a real PYQ
Biogas is generated from organic waste by a process of
- (a)aerobic combustion
- (b)anaerobic decomposition
- (c)photosynthesis
- (d)electrolysis
Answer(b) anaerobic decomposition — decay of organic matter in the absence of oxygen.