Biogas is considered to be an excellent fuel which burns without smoke. The main constituent of biogas is :
- A.methane
- B.hydrogen
- C.carbon dioxide
- D.hydrogen sulphide
Correct answer
Explanation
The correct answer is A, methane. Biogas is mostly methane, usually about 50 to 75 percent, and it is the methane that burns with a clean blue flame and no smoke.
Biogas is made when cattle dung, kitchen waste or crop residue is broken down by anaerobic bacteria (methanogens) in a closed digester without oxygen. Besides methane, the gas contains about 25 to 50 percent carbon dioxide and small traces of hydrogen sulphide, hydrogen and nitrogen. A biogas plant gives a fuel for cooking and lighting and also leaves behind slurry that is a nitrogen-rich manure. Compressed and purified biogas, called Compressed Bio-Gas (CBG), can be used in vehicles in place of CNG.
B is wrong: hydrogen is present only in traces.
C is wrong: carbon dioxide is the second largest part of biogas, but it does not burn.
D is wrong: hydrogen sulphide is a small impurity that gives a rotten-egg smell.
Exam tip: Biogas and CNG are both mainly methane; LPG is mainly butane and propane.
Practice Questions
View allConsider the following animals :
1. Hedgehog
2. Marmot
3. Pangolin
To reduce the chance of being captured by predators, which of the above organisms rolls up/roll up and protects/protect its/their vulnerable parts?
- A.1 and 2
- B.2 only
- C.3 only
- D.1 and 3
Show answer
Hedgehogs and pangolins curl into a tight ball when threatened, covering the soft belly and face with spines or scales; marmots do not.
Read the full explanation →Which one of the following is used in preparing a natural mosquito repellent?
- A.Congress grass
- B.Elephant grass
- C.Lemongrass
- D.Nut grass
Show answer
Lemongrass and its close relative citronella grass yield aromatic oils that keep mosquitoes away, so they are the base of many natural repellents.
Read the full explanation →Which one of the following devices is non-ohmic ?
- A.Conducting copper coil
- B.Electric heating coil
- C.Semi conductor diode
- D.Rheostat
Show answer
A diode does not obey Ohm's law: the current through it is not proportional to the voltage across it. An ohmic conductor gives a straight-line graph of current against voltage, so its resistance stays constant at a fixed temperature.
Read the full explanation →What is the formula mass of anhydrous sodium carbonate? (Given that the atomic masses of sodium, carbon and oxygen are 23 u, 12 u and 16 u respectively)
- A.286 u
- B.106 u
- C.83 u
- D.53 u
Show answer
Anhydrous sodium carbonate is Na₂CO₃, and 2 × 23 + 12 + 3 × 16 = 106 u. Formula mass is the sum of the atomic masses of all the atoms in one formula unit of an ionic compound.
Read the full explanation →Which one of the following minerals is used as a fuel in nuclear power stations ?
- A.Bauxite
- B.Quartz
- C.Feldspar
- D.Pitchblende
Show answer
Pitchblende, or uraninite, is the chief ore of uranium, the fuel used in most nuclear power stations. Pitchblende is a heavy, black mineral made mostly of uranium oxide.
Read the full explanation →