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 21–30 of 39 questions
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UPSC 2019Environment and Ecology · Pollution
Q21. Why is there a great concern about the ‘microbeads’ that are released into the environment?
Explanation
Microbeads are manufactured solid plastic particles of less than one millimetre in their largest dimension. They are most frequently made of polyethene but can be of other petrochemical plastics such as polypropylene and polystyrene. They are used in exfoliating personal care products, toothpaste and in biomedical and health-science research.
Option (a) is correct: Microbeads can cause plastic particle water pollution and pose an environmental hazard for aquatic animals in freshwater and ocean water. NGT had earlier directed the GoI to test cosmetic products containing microbeads after a plea sought a ban on their use on the ground they are extremely dangerous for aquatic life and the environment.
UPSC 2019Environment and Ecology · Pollution
Q22. Which of the following statements are correct about the deposits of ‘methane hydrate’? 1. Global warming might trigger the release of methane gas from these deposits. 2. Large deposits of ‘methane hydrate’ are found in Arctic Tundra and under the seafloor. 3. Methane in the atmosphere oxidised to carbon dioxide after a decade or two. Select the correct answer using the code given below.
Explanation
Methane hydrate is an ice-like substance formed when CH₄ and water combine at low temperature (up to 250C) and moderate pressure (greater than 3-5 MPa, which corresponds to combined water and sediment depths of 300 to 500 m).
Statement 1 is correct: Owing to the melting of ice, global warming might trigger the release of methane gas from these deposits hence having a significant impact on climate change.
Statement 2 is correct: Sediment and sedimentary rock units below Arctic permafrost have the temperature and pressure conditions suitable for the formation and stability of methane hydrate.
Statement 3 is correct: Methane is relatively short-lived in the atmosphere; a molecule of methane is oxidised to water and carbon dioxide within a decade or so, mainly by reaction with other trace gases.
UPSC 2019Environment and Ecology · Pollution
Q23. Consider the following: 1. Carbon monoxide 2. Methane 3. Ozone 4. Sulphur dioxide Which of the above are released into the atmosphere due to the burning of crop/biomass residue?
Explanation
Burning stubble (parali) is the process of removing crop residue from the field in order to prepare it for the next crop. Open stubble burning releases a lot of harmful pollutants into the air, including smoke, particles, greenhouse gases (CO₂, N₂O, O₃ CH₄), air pollutants (CO, NH₃, NOx, SO₂, NMHC), and volatile organic compounds. These pollutants are dangerous to human health. Husk burning reduces the fertility of the soil by destroying its nutrients. When stubble burns, heat is produced that permeates the soil, causing the loss of moisture and beneficial microbes.
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: CO or O₃ are NOT released in crop burning? Absurd, unlikely.
UPSC 2018Environment and Ecology · Pollution
Q24. Which of the following is/are the possible consequence/s of heavy sand mining in river beds? 1. Decreased salinity in the river 2. Pollution of groundwater 3. Lowering of the water-table Select the correct answer using the code given below:
Explanation
Sand mining is the extraction of sand, mainly through an open pit (or sandpit) but sometimes mined from beaches and inland dunes or dredged from ocean and river beds.
Statement 1 is incorrect: Sand mining typically does not directly affect the salinity of the river. Salinity is more influenced by factors like the influx of seawater in coastal areas, evaporation rates, and the presence of saline minerals in the riverbed.
Statement 2 is correct: The amount of suspended particles in the water at the excavation site and downstream increases due to increased riverbed and bank erosion. This process stirs up the sediments and increases the chance of contamination of groundwater.
Statement 3 is correct: Heavy sand mining causes removal of sand and gravels from the riverbed. Due to this the groundwater table drops leaving the drinking water wells on the embankments of these rivers dry. Alteration of rivers, damage to river biodiversity, altered sediment budget lead to poor water quality, worsen water scarcity threat to coastal communities, damage to public and private property.
UPSC 2017Environment and Ecology · Pollution
Q25. Biological Oxygen Demand (BOD) is a standard criterion for:
Explanation
BOD measures the amount of dissolved oxygen required by microorganisms to break down organic material in water over a specific time. BOD is the amount of dissolved oxygen needed by bacteria in decomposing the organic wastes present in water. It is measured in milligrammes per litre of water of oxygen. The higher value of BOD indicates low (Dissolved Oxygen) DO content of water. BOD is not a reliable method for assessing water pollution because it only includes biodegradable elements.
Additional insight:
Standard Method 5210B is the most widely used method for determining Biological Oxygen Demand (BOD). It measures the difference in dissolved oxygen (DO) over a five-day incubation period at 20°C. The initial DO is recorded, and after incubation, the final DO is measured. The BOD value is then calculated based on oxygen depletion. Higher BOD indicates poor water quality due to higher oxygen demand, while lower BOD suggests purer water with less oxygen consumption. DO levels are lower in summer as warm water holds less oxygen.
UPSC 2017Environment and Ecology · Pollution
Q26. In the context of solving pollution problems, what is/are the advantage/advantages of bioremediation techniques? 1. It is a technique for cleaning up pollution by enhancing the same biodegradation process that occurs in nature. 2. Any contaminant with heavy metals such as cadmium and lead can be readily and completely treated by bioremediation using microorganisms. 3. Genetic engineering can be used to create microorganisms specifically designed for bioremediation. Select the correct answer using the code given below:
Explanation
Bioremediation is a branch of biotechnology that employs the use of living organisms in the removal of contaminants, pollutants, and toxins from soil, water, and other environments. These organisms can include microbes and bacteria. As a result, compared to other cleanup techniques, bioremediation causes less disruption to the neighbourhood communities.
Statement 1 is correct: Bioremediation uses naturally occurring organisms to break down hazardous substances into less toxic or non-toxic substances.
Statement 2 is incorrect: Not all contaminants are easily treated by bioremediation using microorganisms. For eg. Heavy metals such as cadmium and lead are not readily absorbed or captured by microorganisms.
Statement 3 is correct: The use of genetic engineering to create organisms specifically designed for bioremediation has great potential. For e.g. Alcanivorax, a bacteria with oil-eating abilities, can be used to create species that are much more capable of cleaning oil spills.
Additional insight:
Types of Bioremediation:
Aerobic Bioremediation: Requires oxygen for microbial reactions, where bacteria use a carbon substrate as an electron donor and oxygen as the electron acceptor to break down contaminants. Anaerobic Bioremediation: Occurs in the absence of oxygen, using alternatives like nitrate, sulfate, or carbon dioxide as electron acceptors. Processes include fermentation, methanogenesis, and reductive dechlorination to degrade pollutants. Cometabolic Bioremediation: Microbes degrade contaminants without gaining energy or carbon from them, breaking down pollutants as a side reaction while metabolizing other substances.
Exam tip:
For S2, "Readily and Completely" treated- it is Clearly an extreme phrase, hence very unlikely to be true. If this would have been true, water and soil pollution would have been talk of past, but that’s not the case, hence likely false. Eliminating options B and D.
UPSC 2017Environment and Ecology · Pollution
Q27. It is possible to produce algae based biofuels, but what is/are the likely limitation(s) of developing countries in promoting this industry? 1. Production of algae based biofuels is possible in seas only and not on continents. 2. Setting up and engineering the algae based biofuels production requires high level of expertise/ technology until the construction is complete. 3. Economically viable production necessitates the setting up of large scale facilities which may raise ecological and social concerns. Select the correct answer using the code given below:
Explanation
Biofuels are hydrocarbon fuel that is created in a short amount of time--days, weeks, or even months--from organic matter (living or once-living material). Biofuels may be solid, liquid or gaseous in nature:
Solid: Wood, dried plant material, and manure Liquid: Bioethanol and Biodiesel Gaseous: Biogas
Statement 1 is incorrect: Algaculture (farming algae) can be initiated on land unsuitable for agriculture or saline water or wastewater. Statements 2 and 3 are correct: Producing algae for biofuels (excluding simple seaweed production) requires significant capital investments, which may be a significant barrier in developing countries that have a weak investment climate. Also during the setup stage, the production of algae- based biofuels will necessitate expertise in advanced technology.
Exam tip:
For S1, "seas ONLY" is an extreme absolute phrase and hence unlikely to be true. Thus eliminate options A and D. In contrast, S 2 and S3 are too general and practical to be false, hence more likely to be true.
UPSC 2016Environment and Ecology · Pollution
Q28. Which of the following best describe/ describes the aim of the ‘Green India Mission’ of the Government of India? 1. Incorporating environmental benefits and costs into the Union and State Budgets thereby implementing the ‘green accounting’ 2. Launching the second green revolution to enhance agricultural output so as to ensure food security to one and all in the future 3. Restoring and enhancing forest cover and responding to climate change by a combination of adaptation and mitigation measures Select the correct answer using the code given below.
Explanation
Green India Mission is one of the eight missions launched under the National Action Plan on Climate Change (NAPCC) with the aim to maintain, restore, and improve India’s dwindling forest cover and combating climate change through a combination of adaptation and mitigation strategies.
Statement 1 and 2 are incorrect: Green accounting is an approach that incorporates environmental costs into financial assessments. The primary goal of green accounting is to help businesses balance economic objectives with environmental considerations. It is not part of the Green India Mission. Facing serious challenges like overproduction of crops like rice and wheat, soil degradation, and food price volatility, the country would need the Second green revolution to focus on the interconnectedness of agriculture, water, and energy to make farming more climate-resilient and environmentally sustainable. Both the statements are irrelevant to the Green India Mission.
Statement 3 is correct: The mission intends to increase forest/ tree cover; improve/enhance ecosystem services and increase the forest-based livelihood income of about 3 million households.
UPSC 2016Environment and Ecology · Pollution
Q29. In the cities of our country, which among the following atmospheric gases are normally considered in calculating the value of the Air Quality Index? 1. Carbon dioxide 2. Carbon monoxide 3. Nitrogen dioxide 4. Sulfur dioxide 5. Methane Select the correct answer using the code given below.
Explanation
There are six AQI categories, namely Good + Satisfactory, Moderately polluted, Poor, Very Poor, and Severe. Each of these categories is decided based on ambient concentration values of air pollutants and their likely health impacts (known as health breakpoints). AQ sub-index and health breakpoints are evolved for eight pollutants, namely:
Ground-level Ozone or O₃ Particulate Matter (PM10 and PM 2.5) Carbon Monoxide or CO Sulphur Dioxide or SO₂ and Nitrogen Dioxide or NO₂ Ammonia (NH₃) Lead (Pb)
UPSC 2014Environment and Ecology · Pollution
Q30. Which of the following are some important pollutants released by the steel industry in India? 1. Oxides of sulphur 2. Oxide of nitrogen 3. Carbon monoxide 4. Carbon dioxide Select the correct answer using the code given below.
Explanation
India is second largest crude steel producer in the world. The steel industry is highly resource and energy-inten-sive, as well as significantly polluting. For instance, India’s current average emission intensity is 2.55 tonnes of CO₂ per tonne of crude steel, while the global average is around 1.95 tonnes. Emissions from the steel sector have decreased by 15% from 2005 to 2022, and the government aims for an additional 10% reduction by 2030. The major environmental impacts of integrated steel mills are from coking and iron-making. Coke production is one of the major pollution sources from steel production. Air emissions such as coke oven gas, naphthalene, ammonium compounds, crude light oil, sulfur and coke dust are released from coke ovens. Steel production has a number of impacts on the environment, including air emissions (CO₂, CO SOx, NOx, PM2.5), wastewater contaminants, hazardous wastes, and solid wastes.
Answer key for these questions
Q
UPSC year
Correct answer
21
2019
(a) They are considered harmful to marine ecosystems.
22
2019
(d) 1, 2 and 3
23
2019
(d) 1, 2, 3 and 4
24
2018
(b) 2 and 3 only
25
2017
(c) Pollution assay in aquatic ecosystems
26
2017
(c) 1 and 3 only
27
2017
(b) 2 and 3 only
28
2016
(c) 3 only
29
2016
(b) 2, 3 and 4 only
30
2014
(d) 1, 2, 3 and 4
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.
