Class 9 Science Chapter 3 Coal and Petroleum: Previous Year Questions with Solved Answers

Re-reading NCERT teaches recognition; solving previous year questions teaches recall and application under time pressure. Here's why PYQs are non-negotiable for Chapter 3: **Examiner Patterns:** CBSE examiners repeat question formats. For example, 'Name one fossil fuel and state its use' has appeared in 2020, 2022, and 2024 papers in nearly identical form. Once you solve it once, you own that question forever. **Confidence in Time Management:** Class 9 exams give limited time. Solving 13 PYQs teaches you how long a 1-mark answer takes (90 seconds), a 3-mark answer (4–5 minutes), and a 5-mark answer (8–10 minutes). You'll never panic on exam day. **Testing Your Weak Spots:** Reading theory feels productive but won't reveal gaps. When you solve a 5-mark question on petroleum refining and stumble on the boiling-point separation concept, you know exactly what to re-study. **Language and Keywords:** Examiners use precise wording. PYQs show you *how* to phrase answers (e.g., "fossil fuels are formed from the decomposition of dead organisms over millions of years") to get full marks rather than 7/10. **Board Pattern Alignment:** CBSE's question paper layout, diagram labels, and mark distribution are visible only in actual papers. Solving PYQs lets you practise under genuine conditions. Start a 3-day free trial at cbsetutor.ai to access video walkthroughs of these questions and get personalized feedback.

1-mark questions test direct recall and definition. Examiners ask these almost every year. **Q1: Define fossil fuels. Give one example.** *Answer:* Fossil fuels are non-renewable energy sources formed from the dead remains of plants and animals buried under the earth millions of years ago. Example: Coal (or petroleum or natural gas). *Why it repeats:* This is the foundational definition. It tests whether you understand that fossil fuels come from ancient life, not minerals. **Q2: Name the process by which coal is formed.** *Answer:* Carbonisation (or coal formation). Carbonisation is the process where plant and animal matter decompose and are compressed under pressure and heat over millions of years to form coal. *Marking tip:* You may earn the mark for either 'carbonisation' alone or 'coal formation'—both are accepted. **Q3: What is the main component of natural gas?** *Answer:* Methane (CH₄) is the main component of natural gas, making up approximately 75–90% of its composition. *Common mistake:* Students confuse LPG (liquefied petroleum gas) with natural gas. Remember: natural gas = methane; LPG = propane and butane mixture. **Q4: Write one use of coal.** *Answer:* Coal is used as a fuel in thermal power plants to generate electricity (or used in industries like iron and steel production, or used domestically for heating). *Variation:* Some papers ask 'Write two uses' (2-mark). Always state the product first, then its use: e.g., "Coal is used in the generation of electricity in thermal power stations." **Q5: Which fraction of petroleum is used as a cooking fuel?** *Answer:* Liquefied Petroleum Gas (LPG) is the fraction of petroleum used as a cooking fuel in households. *Tip:* LPG boils at –42°C, so it remains liquid under pressure in cylinders—this is why it's suitable for cooking. This detail sometimes appears in follow-up questions.

3-mark questions demand explanation and short reasoning. These are the 'sweet spot' for examiners to test process understanding. **Q1: Explain the formation of coal in 3 steps.** *Answer:* Step 1: Millions of years ago, forests (mainly ferns and other plants) were buried under the earth due to volcanic eruptions or other geological changes. Step 2: Buried plant material was subjected to extremely high pressure and temperature over millions of years. Step 3: Gradual decomposition and carbonisation converted these plant remains into coal. (Award 1 mark per step.) *Examiner note:* This question tests chronological and logical understanding. If you answer 'pressure → temperature → coal' without mentioning buried plants first, you lose 1 mark. **Q2: What happens during the fractional distillation of petroleum? Describe the principle.** *Answer:* Fractional distillation separates petroleum into useful fractions based on differences in boiling points. Crude oil is heated to 350°C and vaporised. The vapour enters a fractionating column that is hotter at the bottom and cooler at the top. Components with lower boiling points (like petrol) rise higher and exit at the top; components with higher boiling points (like fuel oil) condense quickly and exit at the bottom. (1 mark for principle, 1 mark for the reason, 1 mark for example/application.) *Key phrase:* Always mention 'boiling point difference' and 'temperature gradient in the column'—examiners check for these exact terms. **Q3: Coal and petroleum are fossil fuels. Why are they called 'non-renewable' resources?** *Answer:* Coal and petroleum are called non-renewable resources because they take millions of years to form from the decomposition of plants and animals under extreme conditions of pressure and temperature. Since we extract and use them much faster than they are naturally produced, they cannot be replenished on a human timescale. Once exhausted, they cannot be replaced. (Award 1 mark for definition, 1 mark for timescale reasoning, 1 mark for implication.) *Challenge variant:* Some papers ask: "Distinguish between renewable and non-renewable energy sources." Be ready to contrast coal with solar or wind. **Q4: What is the difference between LPG and CNG? Name the main component of each.** *Answer:* LPG (Liquefied Petroleum Gas) is a mixture of propane (C₃H₈) and butane (C₄H₁₀), stored as a liquid under pressure. CNG (Compressed Natural Gas) is primarily methane (CH₄), stored as a gas under high pressure. LPG is derived from crude oil refining, while CNG comes from natural gas fields. (1 mark for LPG composition, 1 mark for CNG composition, 1 mark for the key difference.) *Real-world link:* LPG powers cooking cylinders at home; CNG powers cars and buses—this distinction helps memory. **Q5: State any three conservation measures for fossil fuels.** *Answer:* (1) Use of public transport reduces fuel consumption per person. (2) Switching to renewable energy sources like solar and wind power reduces dependence on fossil fuels. (3) Improving industrial efficiency and using energy-efficient appliances reduces fuel wastage. (Or: insulating buildings, carpooling, promoting afforestation to reduce carbon emissions.) (Award 1 mark per measure; 3 marks total.) *Examiners expect:* Specific, actionable measures—not vague ideas like 'use energy wisely.'

5-mark questions require structured, multi-part answers. These are gatekeepers for scoring above 85 in Science. **Q1: Describe the refining of petroleum (or fractional distillation) in detail. How are different products separated?** *Full Solution:* Petroleum refining is a complex industrial process that separates crude oil into useful products. Here is the complete procedure: **Step 1: Heating** – Crude petroleum is heated to approximately 350–375°C in a furnace. At this temperature, most of the crude oil vaporises. **Step 2: Fractional Distillation Column** – The hot vapour is fed into a tall, cylindrical fractionating column. The column is hotter at the bottom (around 350°C) and cooler at the top (around 40°C). **Step 3: Separation by Boiling Point** – Inside the column, different hydrocarbon molecules separate based on their boiling points: - Molecules with low boiling points (short carbon chains like C₅–C₁₀, e.g., petrol/gasoline) do not condense easily and rise to the cooler top regions, where they exit. - Molecules with high boiling points (long carbon chains like C₂₀+, e.g., bitumen) condense quickly and sink to the hotter bottom, where they exit. - Intermediate molecules (kerosene, diesel) exit at intermediate levels. **Step 4: Cooling and Collection** – As vapours rise and encounter cooler regions, they condense into liquids and are collected through outlet trays at different heights. **Typical Products (from top to bottom):** 1. **Petroleum gas (C₁–C₄)** – Used as cooking fuel (LPG) and in refineries. Boiling point: below 20°C. 2. **Petrol/Gasoline (C₅–C₁₀)** – Used as motor fuel. Boiling point: 40–200°C. 3. **Kerosene/Paraffin (C₁₁–C₁₅)** – Used in lamps, jets, and heating. Boiling point: 200–250°C. 4. **Diesel (C₁₆–C₂₀)** – Used in vehicles and generators. Boiling point: 250–300°C. 5. **Fuel Oil/Heavy Fuel (C₂₀–C₃₀+)** – Used in ships and heating. Boiling point: 300–350°C. 6. **Bitumen (residue, C₃₀+)** – Used in road construction. Boiling point: above 350°C. **Why This Works** – The principle is that hydrocarbons with more carbon atoms have stronger intermolecular forces (van der Waals forces), making them harder to vaporise. Shorter hydrocarbons have weaker forces and remain as vapours longer, rising higher in the column. *(Total 5 marks: 1 for heating, 1 for column description, 2 for separation mechanism and products, 1 for application/why it works.)* --- **Q2: Explain why coal is considered a natural resource. What are the consequences of over-exploitation of coal reserves?** *Full Solution:* **Why Coal is a Natural Resource:** Coal is a natural resource because: 1. It is a naturally occurring substance found within the Earth's crust. 2. It is valuable to humans—it provides energy for electricity generation, heat, and industrial processes. 3. It is extracted directly from nature without significant processing before use (unlike manufactured products). 4. It is essential for meeting global energy demands. **Definition in NCERT Context:** Natural resources are materials or substances that exist in nature and can be used by organisms (including humans) to survive and develop. Coal qualifies because it is non-living, non-manufactured, and energy-rich. **Consequences of Over-exploitation of Coal Reserves:** 1. **Depletion of Reserves** – Coal took millions of years to form. At current extraction rates (we mine ≈8 billion tonnes per year globally), recoverable reserves are estimated to last only 100–150 years. Once exhausted, they cannot be replenished in human lifetimes, leaving future generations without this energy source. 2. **Environmental Degradation** – Coal mining destroys vast tracts of land. Open-pit mining creates deep craters, removes topsoil, and ruins habitats for plants and animals. Underground mining can cause land subsidence (collapse of the earth's surface). 3. **Air Pollution** – Burning coal releases carbon dioxide (CO₂), sulfur dioxide (SO₂), and nitrogen oxides (NOₓ). These gases cause: - Global warming and climate change (CO₂ traps heat). - Acid rain (SO₂ and NOₓ react with water in atmosphere). - Respiratory diseases in humans. 4. **Water Pollution** – Coal mines generate acidic water containing heavy metals like mercury and arsenic. This contaminates groundwater and rivers, affecting drinking water and agriculture. 5. **Loss of Biodiversity** – Large-scale coal mining destroys forests and ecosystems, threatening species extinction. 6. **Energy Insecurity** – Over-reliance on coal without developing alternatives (renewables) makes nations vulnerable to supply disruptions and price volatility. **Solutions (brief):** Shift to renewable energy (solar, wind, hydro), improve energy efficiency, reforest mined areas, enforce strict environmental regulations, and invest in clean coal technology (though imperfect). *(Total 5 marks: 1 for defining natural resource, 1 for coal's relevance, 3 for consequences—aim for 3–4 distinct points with brief explanation each.)* --- **Q3: 'Fossil fuels should be conserved for the future.' Justify this statement with reasons. Suggest any three conservation strategies.** *Full Solution:* **Justification for Conservation:** 1. **Non-renewable Nature** – Fossil fuels (coal, petroleum, natural gas) take millions of years to form from dead organisms under pressure and heat. They cannot be replenished within human timescales. Once we exhaust current reserves, they will be gone forever. 2. **Finite Reserves** – Global proven reserves of coal, oil, and natural gas are finite. At present consumption rates: - Coal reserves: ≈130–150 years remaining. - Crude oil reserves: ≈50–60 years remaining. - Natural gas: ≈50–70 years remaining. Without conservation, we risk complete depletion within a century, leaving future generations without critical energy sources. 3. **Economic Importance** – Fossil fuels power electricity generation, transportation, heating, and manufacturing. They sustain modern economies and living standards. Premature depletion would cause energy crises, unemployment, and economic collapse in countries dependent on them. 4. **Time for Transition** – Renewable energy technologies (solar, wind, hydroelectric) are developing but not yet globally mature. Conservation buys time for research, infrastructure, and scaling of alternatives before fossil fuels run out. 5. **Environmental Mitigation** – Burning fossil fuels releases greenhouse gases causing climate change. Reducing consumption through conservation slows carbon emissions and gives ecosystems time to adapt. **Three Conservation Strategies:** 1. **Promote Renewable Energy Sources** – Invest in solar power, wind turbines, hydroelectric dams, and geothermal energy. Governments should incentivise renewable projects and phase out coal-based power plants gradually. Example: India's target of 500 GW renewable capacity by 2030 reduces coal demand. 2. **Improve Energy Efficiency** – Use energy-efficient appliances (LED bulbs, high-efficiency motors), insulate buildings to reduce heating needs, adopt combined-cycle power plants that use fuel more efficiently. Industries should upgrade machinery to reduce fuel consumption per unit output. 3. **Promote Public Transport and Carpooling** – Encourage use of buses, trains, and metro systems instead of private vehicles. Each person in a bus uses 5–10 times less fuel per km than a private car. Electric vehicles (EVs) powered by renewable electricity further reduce fossil fuel dependence. Carpooling and ride-sharing achieve similar efficiency gains. **Additional Measures (for completeness):** - Afforestation: Trees absorb CO₂, reducing atmospheric greenhouse gas load. - Government regulation: Tax carbon emissions, incentivise clean energy research. - Behaviour change: Reduce unnecessary travel, use energy wisely at home. *(Total 5 marks: 2 for justification with reasons, 3 for strategies—aim for clear, distinct, and actionable suggestions.)*

The 2024–25 CBSE Class 9 Science syllabus remains aligned with NCERT Chapter 3 but shows subtle question pattern shifts worth noting: **1. Increased Focus on Conservation and Sustainability** – Older papers (2020–21) asked more definition-based 1-mark questions ('Define fossil fuels'). Recent papers (2023–25) emphasize real-world application: 'Why is petroleum called a fossil fuel?' and 'Suggest measures to conserve natural resources.' Expect 5-mark questions about environmental impact and alternative energy. **2. Diagram-Based Questions on Fractional Distillation** – Examiners now include labelled diagrams of the fractionating column and ask: 'Label the outlets for different fractions' or 'Explain why kerosene condenses at a mid-level.' Be ready to draw and annotate the apparatus, not just describe it in words. **3. Integrated Questions Linking Chapters** – Chapter 3 is now often paired with Chapter 1 (Matter in Our Surroundings) to ask: 'Petroleum is a mixture of hydrocarbons. Why is it called a mixture, and how are its components separated?' This tests understanding across chapters. **4. Climate-Change Connection** – Expect more questions like: 'How does burning fossil fuels contribute to global warming?' and 'Compare the carbon footprint of coal vs. solar energy.' This reflects the National Curriculum Framework's emphasis on environmental literacy. **5. Shorter, Direct Answers Expected** – The 2024–25 papers reward concise, precise answers. Examiners mark strictly on word count and relevance—a 5-mark answer should be 120–150 words, not 200. Rambling explanations cost marks for 'unnecessary information.' **6. Calculation-Based Questions Emerging** – A few recent papers include: 'If a thermal power plant consumes 500 tonnes of coal per day to generate 100 MW of electricity, calculate the efficiency' or 'How much LPG is extracted from 1 tonne of crude oil?' Practise unit conversions and basic arithmetic with energy figures. **What This Means for You:** Focus on explaining *why* (mechanisms, processes) rather than just *what* (definitions). Prepare diagram labels and practice writing concise 5-mark answers. Study renewable energy alternatives alongside fossil fuels—they're no longer just bonus content.

Time management and strategic answering are as important as knowledge. Here's the exact approach used by Class 9 toppers: **Before the Exam (1–2 weeks prior):** 1. Solve all 13 PYQs in this guide under timed conditions. 1-mark questions: 90 seconds each. 3-mark questions: 5 minutes each. 5-mark questions: 8–10 minutes each. This builds muscle memory. 2. Create a one-page summary table: fossil fuel, how formed, boiling point range, uses, conservation method. Revise this daily. 3. Draw the fractionating column from memory at least 5 times until you can label all fractions, boiling points, and products without hesitation. **During the Exam:** 1. **Read the Question Twice** – Many students lose marks by missing keywords. If the question asks 'Name one fossil fuel and state its use,' write both. If it asks only 'Name,' don't explain. 2. **Allocate Time Based on Mark Distribution** – If the paper is 80 marks and lasts 2.5 hours: - 1-mark questions: 1.5 minutes each (including reading and thinking). - 3-mark questions: 5 minutes each. - 5-mark questions: 10 minutes each. If Chapter 3 has 8 marks total (e.g., one 1-mark, one 3-mark, one 5-mark—rare, but totals 9), allocate 16 minutes max. 3. **Answer Familiar Questions First** – If you're confident about coal formation and natural gas, answer those before tackling fractional distillation. This builds confidence and ensures you get 'easy' marks. 4. **Structure 5-Mark Answers** – Always use: - **Opening line:** 1 sentence defining or introducing the concept. - **Body:** 3–4 distinct points, each on a new line, numbered or bulleted. - **Closing line (if space):** 1 sentence linking to real-world impact or summary. Example: "Petroleum refining separates crude oil into products based on boiling points. [Point 1] Crude oil is heated to 350°C. [Point 2] The vapour enters a fractionating column hotter at the bottom and cooler at the top. [Point 3] Molecules with low boiling points rise to the top; those with high boiling points sink to the bottom. [Point 4] This allows separation of petrol, kerosene, diesel, and other fractions." 5. **Use Keywords Correctly** – Examiners scan for keywords like 'millions of years,' 'pressure and temperature,' 'boiling point difference,' 'non-renewable,' 'carbonisation.' If you use these, you're signalling that you understand the concept. 6. **For Diagram Questions:** Draw the fractionating column with vertical arrow showing temperature gradient, horizontal arrows or labels for products, and boiling-point ranges. Even a rough, labelled diagram earns 2–3 marks if you identify all six fractions correctly. 7. **Don't Leave Blanks** – If unsure, write a partial answer. A 3-mark question answered with only half the content earns 1–2 marks, not zero. Blank questions earn zero. **After Marking (Review for Retakes/Higher Levels):** - Identify if you lost marks due to incomplete knowledge (read more) or poor time management (practise faster) or careless reading (slow down next time). - For 5-mark questions, count your word count. Aim for 120–150 words to avoid 'unnecessary information' penalty. **Pro Tip:** Practise at least 3 full mock exams using actual CBSE question papers from the past 3 years. This trains your brain to recognize patterns and manage stress under timed conditions. cbsetutor.ai offers full-length mock tests with instant feedback and video solutions—try a free mock today.

**Fossil Fuels:** Coal, crude petroleum (oil), natural gas—formed from dead organisms over millions of years under extreme pressure and temperature. **Coal Formation (Carbonisation):** Plant matter → buried → compressed over millions of years → coal (mostly carbon). **Natural Gas Main Component:** Methane (CH₄), ≈75–90%. **Petroleum Fractions (in order of boiling point, bottom to top in the column):** | Fraction | Boiling Point (°C) | Uses | Colour | |----------|------|------|--------| | Bitumen (residue) | 350+ | Road surfacing, waterproofing | Black, sticky | | Fuel oil / Heavy fuel | 300–350 | Ship engines, large heating systems | Dark brown | | Diesel | 250–300 | Vehicles, generators, power plants | Pale yellow | | Kerosene / Paraffin | 200–250 | Lamps, jet fuel, heating | Colourless to pale yellow | | Petrol / Gasoline | 40–200 | Car engines, motorcycles | Colourless, volatile | | LPG (propane + butane) | < 20 | Cooking fuel, lighter | Colourless gas under pressure | | Petroleum gas | < 0 | Refinery fuel, power plants | Colourless gas | **Why Fractional Distillation Works:** Hydrocarbons with longer carbon chains have stronger intermolecular forces → higher boiling points → condense at hotter (lower) regions. Short-chain hydrocarbons have weaker forces → lower boiling points → remain as vapours, rise to cooler (higher) regions. **Conservation Strategies:** 1. Renewable energy (solar, wind, hydro, geothermal). 2. Energy efficiency (LED bulbs, insulation, efficient motors). 3. Public transport, carpooling, electric vehicles. 4. Afforestation, controlled industrial emissions, behaviour change. **Why Non-renewable:** Takes millions of years to form; extracted much faster than produced naturally; cannot be replenished on human timescales. **Global Reserve Estimates:** - Coal: 130–150 years at current consumption. - Crude oil: 50–60 years. - Natural gas: 50–70 years. **Environment Impact:** Burning fossil fuels releases CO₂ (greenhouse gas → global warming), SO₂, NOₓ (acid rain), soot (air pollution), heavy metals in mining runoff (water pollution). **CNG vs LPG:** - **CNG:** Compressed Natural Gas, mostly methane (CH₄), from natural gas fields, powers vehicles and buses, high pressure (200–250 bar), cleaner combustion. - **LPG:** Liquefied Petroleum Gas, propane (C₃H₈) + butane (C₄H₁₀), from crude oil refining, powers cooking cylinders, liquefied under moderate pressure (8–12 bar), portable.