Air Pollution (Sources, Control Devices, and CNG Case Study)

Attempt the quiz above first, then review every question with its correct answer and a short explanation below.

1. Q1.According to the Central Pollution Control Board (CPCB) of India, what size of particulate matter (in diameter) is responsible for causing the greatest harm to human health?

   • A.10 micrometers or less
   • B.2.5 micrometers or less (PM2.5)✓ Correct Answer
   • C.5.0 micrometers or less
   • D.1.0 millimeter or less

   Explanation: NCERT Class 12 Biology Chapter 16 states: 'According to Central Pollution Control Board (CPCB), particulate size 2.5 micrometers or less in diameter (PM 2.5) are responsible for causing the greatest harm to human health.' They can be inhaled deep into the lungs, causing inflammation and premature deaths.

2. Q2.Which of the following air pollution control devices can remove over 99 percent of particulate matter present in the exhaust from a thermal power plant?

   • A.Scrubber
   • B.Electrostatic Precipitator (ESP)✓ Correct Answer
   • C.Catalytic Converter
   • D.Cyclone Separator

   Explanation: NCERT documents: 'There are several ways of removing particulate matter; the most widely used of which is the electrostatic precipitator, which can remove over 99 per cent particulate matter present in the exhaust from a thermal power plant.'

3. Q3.In an electrostatic precipitator, electrode wires maintained at several thousand volts produce a corona that releases electrons. These electrons attach to dust particles to give them a:

   • A.Positive charge
   • B.Negative charge✓ Correct Answer
   • C.Neutral state
   • D.Magnetic property

   Explanation: In an ESP, electrode wires release electrons that attach to dust particles, giving them a net negative charge. Grounded collecting plates then attract these negatively charged dust particles, removing them from the air flow (NCERT).

4. Q4.Which air pollution control device is specifically designed to remove harmful gases like sulfur dioxide (SO2) from industrial exhaust?

   • A.Electrostatic Precipitator
   • B.Scrubber✓ Correct Answer
   • C.Catalytic Converter
   • D.Baghouse filter

   Explanation: NCERT Class 12 Biology states: 'A scrubber can remove gases like sulphur dioxide. In a scrubber, the exhaust is passed through a spray of water or lime.' The SO2 reacts with lime to form a calcium sulfite/sulfate precipitate.

5. Q5.What expensive metals are used as catalysts in Catalytic Converters fitted in motor vehicles to reduce toxic emissions?

   • A.Gold and Silver
   • B.Platinum, Palladium, and Rhodium✓ Correct Answer
   • C.Copper, Iron, and Zinc
   • D.Aluminum and Nickel

   Explanation: NCERT Class 12 Biology Chapter 16 states: 'Catalytic converters, having expensive metals namely platinum-palladium and rhodium as the catalysts, are fitted into automobiles for reducing emission of poisonous gases.'

6. Q6.Why should motor vehicles equipped with catalytic converters strictly use unleaded petrol?

   • A.Leaded petrol clogs the vehicle fuel tank.
   • B.Lead in the petrol inactivates the expensive metal catalysts in the converter.✓ Correct Answer
   • C.Leaded petrol releases bad smell from exhaust.
   • D.Unleaded petrol is cheaper.

   Explanation: NCERT Chapter 16 warns: 'Motor vehicles equipped with catalytic converter should use unleaded petrol because lead in the petrol inactivates the catalyst.' This prevents the conversion of carbon monoxide and hydrocarbons into safer gases.

7. Q7.In a catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water, while carbon monoxide and nitric oxide are changed into:

   • A.Sulfur dioxide and oxygen
   • B.Carbon dioxide and Nitrogen gas✓ Correct Answer
   • C.Methane and ozone
   • D.Hydrogen sulfide and carbon

   Explanation: NCERT Chapter 16 states: 'As the exhaust passes through the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water, and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas, respectively.'

8. Q8.In the 1990s, Delhi was ranked fourth among the 41 most polluted cities in the world. To combat this, the Supreme Court directed the government to switch the entire public transport bus fleet to which fuel by the end of 2002?

   • A.Unleaded Diesel
   • B.Compressed Natural Gas (CNG)✓ Correct Answer
   • C.Liquid Petroleum Gas (LPG)
   • D.Ethanol-blended petrol

   Explanation: NCERT Chapter 16 documents Delhi's air pollution control case study: 'All the buses of Delhi were converted to run on CNG by the end of 2002, under the directions of the Supreme Court of India.'

9. Q9.Why is Compressed Natural Gas (CNG) considered a cleaner and better fuel than diesel or petrol for public transport?

   • A.CNG burns most efficiently, leaving very little unburnt, and cannot be easily siphoned off or adulterated.✓ Correct Answer
   • B.CNG does not produce any carbon dioxide upon burning.
   • C.CNG is a liquid that can be mixed with water.
   • D.CNG contains high levels of lead that improves engines.

   Explanation: NCERT Class 12 Biology states: 'CNG is better than diesel or petrol because CNG burns most efficiently, unlike petrol or diesel, in the automobiles and very little of it is left unburnt. Moreover, CNG is cheaper... cannot be siphoned off by thieves and adulterated like petrol or diesel.'

10. Q10.What was the main operational challenge faced by the government while implementing the switch to CNG buses in Delhi?

    • A.CNG caused engines to catch fire easily.
    • B.The difficulty of laying down pipelines to deliver CNG through distribution pumps and ensuring uninterrupted supply.✓ Correct Answer
    • C.CNG was highly expensive.
    • D.Public rejected CNG buses.

    Explanation: NCERT documents: 'The main problem with switching over to CNG is the difficulty of laying down pipelines to deliver CNG through distribution pumps/points and ensuring uninterrupted supply.'

11. Q11.Which of the following organic organisms act as highly sensitive bio-indicators of sulfur dioxide (SO2) air pollution and are absent in polluted industrial cities?

    • A.Fungi
    • B.Lichens✓ Correct Answer
    • C.Ferns
    • D.Algae

    Explanation: Lichens are highly sensitive to sulfur dioxide (SO2) because they lack waxy cuticles and absorb minerals directly from the air. High levels of SO2 destroy their chlorophyll, preventing them from surviving in polluted urban or industrial areas, making them excellent indicators of clean air.

12. Q12.Acid Rain is primarily caused by atmospheric chemical reactions involving which two air pollutants?

    • A.Carbon dioxide and Methane
    • B.Sulfur dioxide (SO2) and Nitrogen oxides (NOx)✓ Correct Answer
    • C.Chlorofluorocarbons and Ozone
    • D.Carbon monoxide and hydrogen sulfide

    Explanation: Acid rain is formed when SO2 and NOx emitted from burning fossil fuels react with water, oxygen, and other chemicals in the atmosphere to form sulfuric acid (H2SO4) and nitric acid (HNO3). This lowers the pH of precipitation below 5.6, damaging soils, forests, and aquatic life.

13. Q13.What pH level in rain is generally considered the threshold below which precipitation is classified as 'Acid Rain'?

    • A.Less than 7.0
    • B.Less than 5.6✓ Correct Answer
    • C.Exactly 8.2
    • D.Between 9.0 and 10.0

    Explanation: Normal rainwater is slightly acidic (pH around 5.6) due to dissolved carbon dioxide forming weak carbonic acid. If dissolved sulfur dioxide and nitrogen oxides lower the pH below 5.6, the precipitation is officially classified as acid rain.

14. Q14.Which of the following describes the difference between a primary pollutant and a secondary pollutant?

    • A.Primary pollutants are gaseous, while secondary are always particulate.
    • B.Primary pollutants are emitted directly from sources, while secondary pollutants are formed in the atmosphere through chemical reactions between primary pollutants and other gases.✓ Correct Answer
    • C.Secondary pollutants are harmless compared to primary.
    • D.Primary pollutants are formed in the stratosphere, while secondary are in the troposphere.

    Explanation: Primary pollutants (such as SO2, CO, and soot) enter the air directly from a source (like a factory chimney or tailpipe). Secondary pollutants (such as Ground-level Ozone and PAN - Peroxyacetyl nitrate) are synthesized in the air through chemical and photochemical reactions.

15. Q15.The brown haze typical of photochemical smog in highly polluted urban cities is composed primarily of secondary pollutants formed under the influence of solar light. A key chemical component of this smog is:

    • A.Carbon monoxide
    • B.PAN (Peroxyacetyl Nitrate) and Ground-level Ozone✓ Correct Answer
    • C.Helium gas
    • D.Pure oxygen

    Explanation: Photochemical smog (or Los Angeles smog) is formed when sunlight reacts with primary pollutants like nitrogen oxides (NOx) and volatile organic compounds (VOCs). This creates a mixture of highly toxic secondary pollutants, including ground-level ozone, aldehydes, and PAN (Peroxyacetyl Nitrate), giving the air a brown, irritating haze.

16. Q16.In an electrostatic precipitator, the velocity of air flowing between the collecting plates must be:

    • A.Extremely high to blow dust away
    • B.Low enough to allow the dust particles to fall to the bottom plates✓ Correct Answer
    • C.Varying randomly continuously
    • D.Equal to the speed of sound

    Explanation: NCERT Class 12 Biology states: 'The velocity of air between the plates must be low enough to allow the dust to fall.' If the velocity is too high, the electrostatic attraction will be overridden by wind currents, carrying dust out.

17. Q17.What atmospheric condition occurs when a layer of warm air traps cooler air near the Earth's surface, preventing air pollutants from dispersing and causing severe smog?

    • A.Cyclone
    • B.Temperature Inversion (Atmospheric Inversion)✓ Correct Answer
    • C.Greenhouse warming
    • D.Thermal upwelling

    Explanation: Under normal conditions, warm air rises, dispersing pollutants. During a temperature inversion, a layer of warm air settles over cooler air near the ground. Because the cool air cannot rise past the warm layer, pollutants (soot, gases) are trapped near the surface, causing hazardous air quality.

18. Q18.Which of the following gaseous pollutants binds to human hemoglobin with an affinity 200 times higher than oxygen, causing oxygen deprivation and asphyxiation?

    • A.Carbon dioxide (CO2)
    • B.Carbon monoxide (CO)✓ Correct Answer
    • C.Sulfur dioxide (SO2)
    • D.Methane (CH4)

    Explanation: Carbon monoxide (CO) is a toxic, colorless, odorless gas. It binds tightly to the iron atoms in hemoglobin to form carboxyhemoglobin. Because its binding affinity is ~200 times higher than oxygen, it blocks oxygen transport, starving tissues of oxygen.

19. Q19.What is the primary source of carbon monoxide (CO) gas pollution in urban areas?

    • A.Photosynthesis by ornamental plants
    • B.Incomplete combustion of carbon-based fuels in automobiles and industries✓ Correct Answer
    • C.Decomposition of organic waste in compost pits
    • D.Evaporation of seawater

    Explanation: Carbon monoxide is produced by the incomplete combustion of carbon-containing fuels (gasoline, diesel, coal, wood) due to insufficient oxygen supply. Motor vehicles are the single largest source of CO pollution in cities.

20. Q20.Which of the following is a structural barrier that separates the clean air from the dust-laden air inside an industrial fabric filter device?

    • A.Electrode wires
    • B.Filter bags (Fabric bags)✓ Correct Answer
    • C.Water spray nozzles
    • D.Lime beds

    Explanation: Fabric filters (or baghouses) pass dust-laden industrial gases through woven or felted fabric bags. The fabric acts as a physical barrier that traps the particulate dust on its surface while letting the clean air pass through, achieving high filtration efficiency.