Pollution: UPSC Previous Year Questions (Environment and Ecology)
39 previous year UPSC Prelims questions on pollution are listed here, from 2005 to 2025. UPSC asks about pollutants and their sources, WHO air quality guidelines, plastics in everyday items, mercury from coal, PFAS, copper smelting and methods to reduce air pollution. The explanations name the pollutant, its source and its effect.
Explanations state facts as of the year each question was asked; words like “recently” refer to that year.
Showing 1–10 of 39 questions
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UPSC 2025Environment and Ecology · Pollution
Q1. Consider the following: 1. Cigarette butts 2. Eyeglass lenses 3. Car tyres How many of them contain plastic?
Explanation
Plastics are synthetic polymers widely used in modern products due to their versatility, durability, and cost-effectiveness. Cigarette Butts: Cigarette butts, made of cellulose acetate, are the most littered plastic waste worldwide, with 4.5 trillion butts discarded annually--66% of the 6 trillion cigarettes smoked. Each releases about 15,000 microplastic fibers, leaching nicotine, arsenic, and lead, and takes up to 10 years to degrade. Eyeglass Lenses: Eyeglass lenses are now mostly plastic-- CR-39, polycarbonate (used in 90% of glasses), Trivex, and high-index plastics--preferred for being lightweight, shatter-resistant, and optically clear. Improper disposal contributes to plastic waste, but recycling remains limited. Car Tyres: Car tyres contain 24% synthetic rubber, 19% natural rubber, carbon black, and synthetic fibers like nylon and polyester. Tyre wear particles (TWPs) contribute 10-28% of oceanic microplastics, totaling 1.2-2.8 million tonnes annually. Hence, option (c) is correct.
Additional insight:
Microplastics, fragments of plastic less than 5 mm, originate from primary sources (e.g., microbeads in cosmetics) or secondary sources (e.g., breakdown of larger plastics like synthetic fabrics or tyres). They are a global pollution threat, found in oceans, air, soil, food, and even human organs, contributing to environmental and health concerns.
Exam tip:
You can try, The "NOT" approach for all statements, this tests the improbability of negating a statement--if denying its impact seems highly unlikely, the statement is plausibly true. For example: Saying "Cigarette butts, Eyeglass lenses or car tyres do not contain plastic" seems highly implausible, suggesting that all three do contain plastic.
UPSC 2025Environment and Ecology · Pollution
Q2. Consider the following statements: Statement I: Activated carbon is a good and an attractive tool to remove pollutants from effluent streams and to remediate contaminants from various industries. Statement II: Activated carbon exhibits a large surface area and a strong potential for adsorbing heavy metals. Statement III: Activated carbon can be easily synthesized from environmental wastes with high carbon content. Which one of the following is correct in respect of the above statements?
Explanation
Statement I is correct: Activated carbon is an effective, versatile adsorbent for removing pollutants from effluent streams like wastewater and industrial discharges, widely used in textile, pharmaceutical, and petrochemical industries. It removes organic compounds (e.g., phenols, dyes), heavy metals (e.g., lead, mercury), and VOCs with 90-99% efficiency. The EPA classifies it as a Best Available Technology (BAT) for wastewater treatment.
Statement II is correct: Its large surface area (500-1500 m²/g) and microporous structure (<2 nm pores) offer abundant adsorption sites. Surface functional groups (e.g., hydroxyl, carboxyl) enhance binding of cadmium, chromium, lead, and mercury, with 95-99% removal efficiency. High BET surface area and pore volume (0.5-2 cm²/g) explain its adsorption efficiency, reinforcing Statement I.
Statement III is correct: Activated carbon can be synthesized from environmental wastes (e.g., coconut shells, rice husks, bagasse, fruit peels, sewage sludge) via pyrolysis (400-800°C) and chemical/physical activation. Coconut shells yield >1000 m²/g, bagasse 800-1200 m²/g. This cost-effective, sustainable process supports its use in pollutant removal and aligns with circular economy goals
UPSC 2025Environment and Ecology · Pollution
Q3. Artificial way of causing rainfall to reduce air pollution makes use of
Explanation
Cloud-seeding is a technique used to modify weather by releasing silver iodide (AgI) into the atmosphere to facilitate the formation of ice crystals, enhancing the cloud’s ability to generate rain. In the process of cloud-seeding, chemicals like silver iodide, potassium iodide, and dry ice are dispersed into the sky via airplanes and helicopters.
Additional insight:
Cloud seeding is divided into two main types:
Hygroscopic Cloud Seeding: This approach promotes the growth of water droplets in liquid clouds by introducing salt particles, typically at the cloud’s base, which helps the droplets combine and become heavy enough to fall as rain. Glaciogenic Cloud Seeding: This method encourages the formation of ice crystals in supercooled clouds by releasing substances such as silver iodide or dry ice, which serve as ice nuclei, initiating ice formation and ultimately leading to precipitation.
UPSC 2024Environment and Ecology · Pollution
Q4. With reference to perfluoroalkyl and polyfluoroalkyl substances (PFAS) that are used in making many consumer products, consider the following statements: 1. PFAS are found to be widespread in drinking water, food and food packaging materials. 2. PFAS are not easily degraded in the environment. 3. Persistent exposure to PFAS can lead to bioaccumulation in animal bodies. Which of the statements given above are correct?
Explanation
Per- and polyfluoroalkyl substances (PFAS) are a large, complex group of synthetic chemicals that have been used in consumer products around the world since about the 1950s.
Statement 1 is correct: People are most likely exposed to these chemicals by consuming PFAS-contaminated water or food, using products made with PFAS, or breathing air containing PFAS. Although PFOS use has been phased out, it can still be found in drinking water, groundwater, soil, and air.
Statement 2 is correct: PFAS molecules have a chain of linked carbon and fluorine atoms. Because the carbon-fluorine bond is one of the strongest, these chemicals do not degrade easily in the environment, leading to long-term contamination.
Statement 3 is correct: PFAS can accumulate in the bodies of animals, including humans, through persistent exposure. They tend to concentrate in organs like the liver and kidneys and bio-accumulate up the food chain
UPSC 2024Environment and Ecology · Pollution
Q5. Consider the following statements: Statement-I: Many chewing gums found in the market are a source of environmental pollution. Statement-II: Many chewing gums contain plastic as gum base. Which one of the following is correct in respect of the above statements?
Explanation
Statement I is correct: Chewing gum contributes significantly to environmental pollution due to its non-biodegrad-able nature. Most chewing gums are improperly disposed of, leading to litter on streets and microplastic pollution in water bodies.
Statement II is correct: Modern chewing gums often use synthetic polymers, such as polyethylene and polyvinyl acetate, as part of their gum base, which are essentially plastics. These materials do not biodegrade easily, causing long-lasting environmental harm. The presence of plastic in gum makes it non-biodegradable and a significant contributor to pollution when improperly disposed of. Hence, Both Statement-I and Statement-II are correct and Statement-II explains Statement-I
UPSC 2023Environment and Ecology · Pollution
Q6. Consider the following: 1. Aerosols 2. Foam agents 3. Fire retardants 4. Lubricants In the making of how many of the above are hydrofluorocarbons used?
Explanation
Hydrofluorocarbons (HFCs) are a climate "Super-Pollutant" - Greenhouse gases with hundreds to thousands of times the heat-trapping power of carbon dioxide (CO₂). HFCs are synthetic gases used in air conditioning systems, aerosol propellants, foam- blowing agents, solvents, and flame retardants. These gases were first developed as alternatives to ozone- depleting chemicals, but after their rollout, it was learned that their release to the atmosphere during manufacturing processes and leakage during use, servicing, and retirement/replacement of equipment poses a grave threat to our climate. Lubricants are typically based on oils and synthetic esters, not HFCs.
UPSC 2023Environment and Ecology · Pollution
Q7. Consider the following statements regarding mercury pollution:
Explanation
Statement 1 is correct: Mercury is used in Artisanal Small-Scale Gold Mining (ASGM). The majority of the mercury emissions associated with the ASGM sector come from the burning of mercury-gold amalgam, which is responsible for 38% of all anthropogenic mercury emissions to the atmosphere.
Statement 2 is correct: Mercury is released into the atmosphere via the burning of coal and other fossil fuels. Because coal has far higher mercury content than other fossil fuels, coal-fired power stations frequently produce more mercury pollution than power plants that burn other fossil fuels.
Statement 3 is incorrect: The Occupational Safety and Health Administration (OSHA) considers mercury vapor concentrations above 0.01 mg/m³ hazardous for prolonged exposure, with an acceptable limit of 0.1 mg/m³ based on an 8-hour time-weighted average. Both American Conference of Governmental Industrial Hygienists (ACGIH) and National Institute for Occupational Safety and Health (NIOSH) recommend even lower exposure levels to minimize health risks.
UPSC 2023Environment and Ecology · Pollution
Q8. Consider the following statements: Statement-I: According to the United Nations’ World Water Development Report, 2022’, India extracts more than a quarter of the world’s groundwater withdrawal each year. Statement-II: India needs to extract more than a quarter of the world’s groundwater each year to satisfy the drinking water and sanitation needs of almost 18% of the world’s population living in its Territory. Which one of the following is correct in respect of the above statements?
Explanation
Statement-I is correct: According to the United Nations’ World Water Development Report 2022, India extracts more than a quarter of the world’s groundwater withdrawal each year. This indicates that India has a significant reliance on groundwater resources for various purposes, including irrigation, drinking water, and industrial use. Statement-II is not correct: Approximately 89% of India’s groundwater is utilised for irrigation purposes. The primary portion of the total groundwater extracted in India serves irrigation needs rather than being allocated for drinking and sanitation purposes. Only a small portion of groundwater is utilized for domestic and industrial purposes.
UPSC 2022Environment and Ecology · Pollution
Q9. In the context of WHO Air Quality Guidelines, consider the following statements: 1. The 24-hour mean of PM2.5 should not exceed 15 ug/m3 and annual mean of PM2.5 should not exceed 5 ug/m3. 2. In a year, the highest levels of ozone pollution occur during the period of inclement weather. 3. PM10 can penetrate the lung barrier and enter the bloodstream. 4. Excessive ozone in the air can trigger asthma. Which of the statements given above are correct?
Explanation
The updated (2021) WHO Global Air Quality Guidelines (AQGs) provide recommendations on air quality guideline levels as well as interim targets for six key air pollutants. The guidelines focus on so-called classical pollutants, particulate matter (PM. and PM), ozone (O₃), nitrogen dioxide (NO₂), sulfur dioxide (SO₂) and carbon monoxide (CO).
Statement 1 is correct: The 24-hour ceiling mean of PM 2.5 used to be 25 micrograms but has now dropped to 15.
Statement 2 is incorrect: Ozone at ground level is formed by the reaction with sunlight (photochemical reaction) of pollutants such as nitrogen oxides (NOx) from vehicle and industry emissions and volatile organic compounds (VOCs) emitted by vehicles, solvents and industry. As a result, the highest levels of ozone pollution occur during periods of sunny weather and not during inclement weather.
Statement 3 is incorrect: Particles with a diameter of 10 m (PM10) can reach the lungs but cannot enter the bloodstream. However, particles with a diameter of 2.5 m or less can penetrate deeper into the lungs, reaching the alveoli, enter the bloodstream, and potentially cross blood-organ barriers, impacting various organs such as the brain, heart, liver, and kidneys. PM (10 microns) can reach deep into the lungs, but the more harmful PM. (2.5 microns) can penetrate the lung barrier and enter the bloodstream, posing severe health risks.
Statement 4 is correct: Excessive ozone in the air can have a marked effect on human health. It causes breathing problems, triggers asthma, reduces lung function and causes lung diseases. Ozone triggers asthma because it is very irritating to the lungs and airways.
UPSC 2022Environment and Ecology · Pollution
Q10. Consider the following: 1. Carbon monoxide 2. Nitrogen oxide 3. Ozone 4. Sulphur dioxide Excess of which of the above in the environment is/are the cause(s) of acid rain?
Explanation
Normal rain has a pH of about 5.6 when pH falls below this; it is called Acid rain (pH 4.2 to 4.4). Acid rain results when Sulfur Dioxide (SO₂) & Nitrogen Oxides (NOX) react with water, oxygen & other chemicals to form Sulfuric & Nitric acids. Nitrous oxide and Sulphur dioxide cause Acid rain. The acid rain harms microorganisms in the soil; inhibits the activity of nitrogen fixation bacteria; soil acidification; ocean acidification; affects the growth of plants; food chain; kills aquatic animals; corrosion of metals & weathering of stone buildings & statues. NOx + SO₂ + Moisture + other chemicals Acid Rain (HNO₃ + H₂ SO₄)
Answer key for these questions
Q
UPSC year
Correct answer
1
2025
(c) All the three
2
2025
(a) Both Statement II and Statement III are correct and both of them explain Statement I
3
2025
(a) silver iodide and potassium iodide
4
2024
(d) 1, 2 and 3
5
2024
(a) Both Statement-I and Statement-II are correct and Statement-II explains Statement-I
6
2023
(c) Only three
7
2023
(b) Coal-based thermal power plants cause mercury pollution.
8
2023
(c) Statement-I is correct but Statement-II is incorrect
9
2022
(b) 1 and 4 only
10
2022
(b) 2 and 4 only
What UPSC has tested in Pollution
Cigarette butts, eyeglass lenses and car tyres all contain plastic.
Artificial rain to reduce air pollution uses silver iodide and potassium iodide.
Coal-based thermal power plants are a major source of mercury pollution.
PFAS are widespread in drinking water, food packaging and consumer products, and are not easily degraded.
Frequently asked questions
How many previous year UPSC questions are there on Pollution?
This page covers 39 previous year UPSC Prelims GS Paper-I questions on Pollution (Environment and Ecology), asked from 2005 to 2025. Each has the correct answer and an explanation.
Which common items contain plastic?
Cigarette butts, whose filters are made of cellulose acetate, a plastic; eyeglass lenses, which are often plastic polymers; and car tyres, which contain synthetic rubber and microplastic-shedding polymers.
What are PFAS?
Per- and polyfluoroalkyl substances, a large group of synthetic chemicals used in non-stick, waterproof and firefighting products. They are called forever chemicals because they resist breakdown and can build up in animal bodies.
Which chemicals are used in cloud seeding?
Silver iodide and potassium iodide, besides dry ice. They act as nuclei around which ice crystals form, helping clouds produce rain, and they are tried as a way of washing pollutants out of the air.
