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Environment & ecology

Prelims · Environment & ecology · 40 questions

Pollution & waste

Every UPSC Prelims question on this topic, 2016–2026, newest first. Tap an option to check yourself; the answer and explanation open below it.

Pollution & waste questions per year: 2016: 1, 2017: 2, 2018: 1, 2019: 5, 2020: 2, 2021: 6, 2022: 3, 2023: 2, 2024: 4, 2025: 4, 2026: 0 Asked in 10 of 11 years · most in 2021 (6)

UPSC syllabus: “General issues on Environmental ecology, Bio-diversity and Climate Change - that do not require subject specialization.” See the full syllabus →

Prelims 2020 · Q48

Medium

Which of the following are the reasons/factors for exposure to benzene pollution?

  1. 1.Automobile exhaust
  2. 2.Tobacco smoke
  3. 3.Wood burning
  4. 4.Using varnished wooden furniture
  5. 5.Using products made of polyurethane

Select the correct answer using the code given below:

Answer & explanation

Answer: (a) 1, 2 and 3 only

Benzene is a volatile chemical released when fuels and other organic material burn, so vehicle exhaust, tobacco smoke and wood burning are all recognised sources of exposure. Varnished wooden furniture and polyurethane products are not named in the official lists of benzene sources.

  • ✓ 1. Benzene is present in motor vehicle exhaust and in petrol (gasoline) vapour.
  • ✓ 2. Tobacco smoke contains benzene, and WHO calls active and passive smoke exposure a significant source of exposure.
  • ✓ 3. Wood-burning fires are named among the common sources of benzene in air.
  • ✗ 4. UPSC's key does not count this as a benzene source. EPA's summary names glues, paints and furniture wax among household sources, but not varnished wooden furniture itself.
  • ✗ 5. Polyurethane products are not named among the recognised benzene sources in the EPA and WHO summaries, and UPSC's key does not count them.

Remember · Benzene comes from burning and fuels: vehicle exhaust, tobacco smoke, wood-burning fires, petrol vapour, and some glues and paints.

Sources

  • US EPA, Benzene TEACH Chemical Summary ↗ “Benzene is an organic compound found most often in air as a result of emissions from burning coal and oil, gasoline vapors at gasoline service stations, motor vehicle exhaust, cigarette smoke, wood-burning fires, some adhesives, and other sources … Sources include cigarette smoke; exhaust from motor vehicles; smoke from wood burning fires; and some household products which contain petroleum-based chemicals such as glues, paints, furniture wax, and lubricants.”
  • WHO, Exposure to benzene: a major public health concern ↗ “Active and passive exposure to tobacco smoke is also a significant source of exposure.”

Question and answer: UPSC's official GS Paper I (2020, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 1 Oct 2026 (how we verify). Permalink ·

Prelims 2020 · Q76

Medium

Steel slag can be the material for which of the following?

  1. 1.Construction of base road
  2. 2.Improvement of agricultural soil
  3. 3.Production of cement

Select the correct answer using the code given below:

Answer & explanation

Answer: (d) 1, 2 and 3

Steel slag, the solid waste left when steel is made, is usable in all three ways: as stone-like aggregate in road layers, as a soil conditioner in farming, and as an ingredient in cement.

  • ✓ 1. Processed steel slag replaces natural stone aggregate in roads; CSIR-CRRI has framed guidelines for using it in various road works, and a six-lane highway near Surat was built with it.
  • ✓ 2. The Ministry of Steel lists agriculture as a use, where the slag stands in for soil nutrients and fertilisers, and its website mentions soil conditioning.
  • ✓ 3. The Ministry of Steel names 'green cement' among the uses of steel slag; note that blast-furnace (iron) slag is the type mostly used in cement making today.

Remember · Steel slag is a waste-to-wealth material: road aggregate, soil conditioner, cement ingredient and rail ballast.

Sources

Question and answer: UPSC's official GS Paper I (2020, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink ·

Prelims 2020 · Q79

Easy

Consider the following statements:

  1. 1.Coal ash contains arsenic, lead and mercury.
  2. 2.Coal-fired power plants release sulphur dioxide and oxides of nitrogen into the environment.
  3. 3.High ash content is observed in Indian coal.

Which of the statements given above is/are correct?

Answer & explanation

Answer: (d) 1, 2 and 3

All three statements are correct: coal ash carries toxic trace metals such as arsenic, lead and mercury, coal-burning power plants emit sulphur dioxide and nitrogen oxides, and Indian coal is high in ash.

  • ✓ 1. Coal and its fly ash hold toxic trace elements; the US Geological Survey names arsenic, selenium, lead and mercury among those tested in fly ash.
  • ✓ 2. CPCB's standards for coal-based thermal power plants set limits for sulphur dioxide and oxides of nitrogen in the flue gas, because burning coal releases both.
  • ✓ 3. The Ministry of Coal states that coal produced in India generally has 25 to 45 per cent ash, against 10 to 20 per cent for imported coal, which is why washing of coal is promoted.

Remember · Coal power means SO2 and NOx in the air and ash laden with arsenic, lead and mercury on the ground; Indian coal is high in ash.

📘 Read it in NCERT: Class 11 Indian Economic Development, Ch 7 (practise this chapter)

Sources

Question and answer: UPSC's official GS Paper I (2020, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink ·

The same topic in Mains

Read it in NCERT

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