Which one of the following statements about biogas is not correct ?
- A.It is mainly composed of methane gas.
- B.It is a non-renewable source of energy.
- C.It is formed by the decomposition of cow dung in the absence of oxygen.
- D.It burns without smoke and leaves no residue.
Correct answer
Explanation
The correct answer is B, It is a non-renewable source of energy. This statement is wrong: biogas is renewable, because the cattle dung, crop waste and kitchen waste it is made from are produced again and again.
Biogas is made in a digester where bacteria break down organic matter anaerobically, that is, without oxygen. The gas is mostly methane (about 50 to 75 per cent), with carbon dioxide and small amounts of hydrogen and hydrogen sulphide. It is a clean fuel for cooking and lighting in villages: it burns with a blue flame, gives no smoke and leaves no ash. The slurry left in the plant is a nutrient-rich manure, so a biogas plant gives both fuel and fertiliser.
Option A is wrong because methane is indeed the main component. Option C is wrong because anaerobic breakdown of dung is exactly how biogas forms. Option D is wrong because smokeless, residue-free burning is a true feature of biogas.
Exam tip: biogas is renewable, mainly methane, made anaerobically, and gives fuel plus manure.
Practice Questions
View allWhich one of the following statements with regard to growth of coral reefs is not correct?
- A.Coral can grow abundantly in freshwater.
- B.It requires warm water between 23 °C-25 °C.
- C.It requires shallow saltwater, not deeper than 50 metres.
- D.It requires plenty of sunlight to aid photosynthesis.
Show answer
Reef-building corals are marine animals and die in fresh water, so this statement is false. Corals are tiny polyps that build skeletons of calcium carbonate and live with algae called zooxanthellae inside their tissues.
Read the full explanation →Which one of the following biosphere reserves is spread over three States in India?
- A.Nilgiri
- B.Achanakmar-Amarkantak
- C.Seshachalam
- D.Agasthyamalai
Show answer
The Nilgiri Biosphere Reserve spreads across Tamil Nadu, Kerala and Karnataka. Set up in 1986, Nilgiri was India's first biosphere reserve, and in 2000 it became the first Indian reserve on UNESCO's World Network of Biosphere Reserves.
Read the full explanation →Which of the following is/are renewable source(s) of energy? 1. Fossil fuel 2. Biofuel 3. Uranium 4. Hydropower Select the correct answer using the code given below.
- A.2 only
- B.3 and 4
- C.1 and 3
- D.2 and 4
Show answer
Biofuel and hydropower are renewable because nature replaces them within a human lifetime, while fossil fuels and uranium are not.
Read the full explanation →Which one of the following is NOT decomposed by bacterial action ?
- A.Vegetable remains
- B.Plastic materials
- C.Animal carcasses
- D.Wastes of flowers
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Ordinary plastics are non-biodegradable, so bacteria and fungi cannot break them down in any useful length of time. Most plastics, such as polyethylene, polypropylene and PVC, are long synthetic polymers made from petroleum.
Read the full explanation →According to the Environmental Protection Agency (EPA), which one of the following is the largest source of sulphur dioxide emissions?
- A.Locomotives using fossil fuels
- B.Ships using fossil fuels
- C.Extraction of metals from ores
- D.Power plants using fossil fuels
Show answer
The EPA names the burning of fossil fuels by power plants and other industrial facilities as the largest source of sulphur dioxide.
Read the full explanation →