Coal and Petroleum – Case-based Questions with Answers

Class 8 Science | Chapter 5: Coal and Petroleum — 20 Case-Based Questions (NCERT)

CBSE Board Examinations — Systematic overview

Each case links concepts to real-life scenarios: formation, properties, refining, environmental impact, safety and conservation. Questions encourage application, analysis and short structured answers aligned to NCERT.

Case Set A — Formation & Identification (1–5)

Case 1

Rita visits a museum and sees layers of plant fossils in rocks. The guide explains that these remains turned into coal over millions of years.

Q1. Explain briefly the process that transforms plant remains into coal.

A1. Plant remains buried in swampy sediments undergo carbonisation under heat and pressure; stages include peat → lignite → bituminous → anthracite, with increasing carbon content and calorific value.

Case 2

During a science project, Aryan notices black, shiny pieces labelled 'anthracite' and 'lignite' and wonders why they differ.

Q2. State two differences between lignite and anthracite.

A2. Lignite has lower carbon content and higher moisture; anthracite has highest carbon, low volatile matter and burns hotter and cleaner.

Case 3

A geography map shows oil fields offshore. A student asks how oil forms in seas.

Q3. Outline how petroleum (crude oil) is formed from marine organisms.

A3. Dead plankton and marine plants buried under sediments are subjected to heat and pressure over millions of years, transforming into hydrocarbons that migrate and accumulate as crude oil in reservoirs.

Case 4

At a fuel station, Varun sees different fuels labelled petrol and diesel and asks why they are different.

Q4. Give one compositional difference and one use difference between petrol and diesel.

A4. Petrol contains lighter hydrocarbons (shorter chains) and is used in spark-ignition engines; diesel has heavier hydrocarbons and is used in compression-ignition engines for heavy vehicles.

Case 5

A field trip brochure mentions natural gas pipelines delivering 'cleaner fuel' to cities.

Q5. Why is natural gas considered cleaner than coal? Give two reasons.

A5. Natural gas burns with fewer particulates and lower sulfur emissions, producing less smog and acid rain; it typically emits less CO₂ per unit energy compared to coal.

Case Set B — Refining & Fractional Distillation (6–10)

Case 6

A model of a fractionating column is shown in class. The teacher asks students to predict where petrol would be collected.

Q6. Where in a fractionating column is petrol collected and why?

A6. Petrol condenses near the top of the column where temperatures are lower because it has a lower boiling point than heavier fractions.

Case 7

During a lab demonstration, a heavy residue remains at the bottom after distillation of crude oil.

Q7. Name this residue and one of its common uses.

A7. The residue is bitumen (or tar), used for road surfacing and roofing.

Case 8

Students learn that refining removes sulfur from fuels before sale.

Q8. Why is sulfur removed from crude oil fractions?

A8. Sulfur causes SO₂ emissions when burned, leading to acid rain and pollution; removing sulfur protects the environment and prevents catalyst poisoning in engines and refinery units.

Case 9

An industry student asks how refineries increase petrol yield from crude oil.

Q9. Mention one refinery process besides fractional distillation that increases petrol yield.

A9. Cracking breaks large hydrocarbon molecules into smaller ones, increasing petrol and light hydrocarbon yields.

Case 10

A chart shows different uses of petroleum fractions.

Q10. List three fractions obtained from crude oil and one use of each.

A10. Petrol (fuel for cars), kerosene (aviation/household heating), diesel (fuel for heavy vehicles); lubricating oil (machinery lubrication), bitumen (roads).

Case Set C — Environmental Impact & Safety (11–15)

Case 11

A town near a coal-fired power plant reports frequent respiratory complaints.

Q11. Identify two pollutants from coal combustion that could cause respiratory problems.

A11. Particulate matter (soot) and sulfur dioxide (SO₂) irritate lungs and contribute to respiratory illnesses.

Case 12

An oil spill occurs off a coastline, threatening wildlife and fishermens livelihoods.

Q12. Describe two immediate actions taken to reduce environmental damage from oil spills.

A12. Containment using booms to limit spread and skimming to remove oil from the surface; wildlife rescue and shoreline cleanup are also immediate measures.

Case 13

A locality is advised to switch from coal to LPG for domestic cooking.

Q13. Explain one advantage and one precaution when using LPG at home.

A13. Advantage: LPG burns cleaner with less smoke and particulates. Precaution: check for leaks with soapy water and keep cylinders upright in ventilated areas away from heat.

Case 14

A construction company chooses bitumen for road surfacing near a wetland.

Q14. What environmental considerations should be taken when using bitumen in such projects?

A14. Prevent runoff and contamination of wetlands, use proper storage to avoid spills, ensure controlled application to minimise fumes, and follow local environmental guidelines to protect aquatic life.

Case 15

Students compare CO₂ emissions from coal and natural gas for the same energy output.

Q15. Which fuel emits more CO₂ per unit energy and why?

A15. Coal emits more CO₂ per unit energy because it has higher carbon content and less hydrogen relative to natural gas (methane), leading to greater CO₂ on combustion.

Case Set D — Conservation & Alternatives (16–20)

Case 16

A city plans to reduce fossil fuel use by improving public transport and promoting electric buses.

Q16. How will better public transport reduce fossil fuel consumption? Give one social and one environmental benefit.

A16. Social: reduced travel cost and congestion improves accessibility. Environmental: fewer vehicles lower total fuel consumption and emissions, improving air quality.

Case 17

A farmer considers using biogas produced from agricultural waste instead of LPG for cooking.

Q17. Explain briefly what biogas is and one advantage it has over fossil fuels.

A17. Biogas is produced by anaerobic decomposition of organic waste (methane-rich); advantage: renewable and reduces waste while emitting less net CO₂ compared to fossil fuels.

Case 18

A policy maker is discussing energy reserves and resources for long-term planning.

Q18. Define 'reserves' and explain why reserve estimates matter for energy policy.

A18. Reserves are quantities of fuel that can be extracted economically with current technology; they inform planning for energy security, infrastructure investment and transition timelines to alternatives.

Case 19

A school organises an awareness drive to reduce fuel use at home.

Q19. Suggest three simple household measures to conserve fossil fuels.

A19. Use energy-efficient appliances and LED bulbs, prefer public transport or carpooling, and insulate homes to reduce heating/cooling needs.

Case 20

A student reads about 'peak oil' and wonders about its implications.

Q20. What does 'peak oil' refer to and what could be one consequence if demand outstrips reserves?

A20. 'Peak oil' is the point where global oil production reaches its maximum and then declines; consequence: higher prices, supply insecurity and accelerated shift to alternative energy sources.