The Fuel is part of Chemistry. Below are notes on 11 sub-topics, followed by practice MCQs from State PSC and UPSC papers.

Biofuels: First, Second, and Third Generation

  • Biofuels: Fuels derived from biomass (recently living organisms or metabolic byproducts). Renewable alternative to fossil fuels.
  • First Generation Biofuels:
    • Source: Edible food crops (e.g., corn, sugarcane, soybean, palm oil).
    • Examples: Bioethanol (from sugar/ starch fermentation), Biodiesel (from vegetable oil transesterification).
    • Production: Involves chemical changes (e.g., fermentation, transesterification).
    • Challenge: "Food vs. Fuel" debate, land/water use, often limited GHG reduction.
  • Second Generation Biofuels:
    • Source: Non-food biomass (lignocellulosic material like agricultural waste, forest residue, dedicated energy crops).
    • Examples: Cellulosic ethanol, Biodiesel from non-edible oils (e.g., Jatropha). Biogas from anaerobic digestion is often grouped here.
    • Production: More complex chemical processes (e.g., enzymatic hydrolysis, gasification followed by FischerTropsch synthesis, anaerobic digestion).
    • Advantage: Utilizes waste, avoids food vs. fuel conflict, potentially greater GHG reduction.
    • Challenge: Expensive, complex technology, lower yields than 1st Gen.
  • Third Generation Biofuels:
    • Source: Algae and other microbes.
    • Examples: Algae-based biodiesel, bioethanol, biojet fuel.
    • Production: Cultivation of algae, followed by extraction of lipids or fermentation of carbohydrates. These are chemical changes.
    • Advantage: High yield per unit area, non-arable land use, consumes CO2, potentially uses wastewater.
    • Challenge: High capital and operating costs, scalability issues.
  • Biogas: Produced via anaerobic digestion of organic matter (e.g., animal waste, agricultural residues). This decomposition process, leading to the formation of methane and carbon dioxide, is a chemical change.
  • Combustion of Biofuels: The process of burning biofuels (e.g., biogas as fuel) is a chemical change, as it involves a chemical reaction with oxygen, producing new substances (e.g., CO2, H2O) and releasing energy.

Calorific Value and Fuel Efficiency

  • Calorific Value (Fuel Value): The total heat energy produced when a unit mass (or volume) of fuel undergoes complete combustion.
  • Unit of Calorific Value: Expressed in kilojoules per kilogram (kJ/kg) or kilojoules per gram (kJ/g).
  • Fuel Efficiency: Directly proportional to calorific value; a higher calorific value indicates greater fuel efficiency.
  • Approximate Calorific Values (kJ/g):
    • Hydrogen: ~150
    • Methane (main component of Natural Gas): ~55
    • Butane: ~49.5
    • Gasoline: ~45-48
    • Charcoal: ~33
    • Ethanol: ~29.7
  • Hydrogen possesses the highest calorific value (~150 kJ/g) among commonly known fuels.

Combustion: Types, Mechanism, and Products

  • Combustion: An exothermic chemical process involving rapid reaction between a substance (fuel) and an oxidant (usually oxygen from air), producing heat and light.
  • Fire Triangle: Three essential components for combustion: Fuel (combustible material), Oxygen (oxidizer), and Heat (to reach ignition temperature). Removing any component extinguishes fire.
  • Types of Combustion:
    • Rapid Combustion: Occurs quickly with distinct heat and light (e.g., burning LPG).
    • Spontaneous Combustion: Occurs without external heating, substance ignites on its own at room temperature (e.g., white phosphorus, coal dust in mines).
    • Explosive Combustion: Very rapid combustion producing large amounts of heat, light, and gas, often accompanied by a sound (e.g., firecrackers).
  • Products of Combustion:
    • Complete Combustion (sufficient oxygen): Carbon dioxide (CO₂) and water (H₂O), heat, and light.
    • Incomplete Combustion (insufficient oxygen): Carbon monoxide (CO), soot (unburnt carbon particles), and less heat.
  • Fire Classification (based on fuel type):
    • Class A: Ordinary Combustibles (solids like wood, paper, cloth, plastics).
    • Class B: Flammable Liquids and Combustible Liquids (e.g., petrol, diesel, oil, grease, paints, solvents, alcohol, molten sulfur).
    • Class C: Flammable Gases (e.g., LPG, natural gas, methane).
    • Class D: Combustible Metals (e.g., magnesium, titanium, sodium, potassium).
    • Class K (or F): Cooking Oils and Fats (e.g., vegetable oils, animal fats in kitchen fires).

Environmental Impact of Fuel Combustion: Pollution, Greenhouse Gases, Acid Rain

  • Historically, petrol (gasoline) combustion in automobiles released lead into the atmosphere due to lead-containing additives (e.g., tetraethyl lead).
  • Hydrogen combustion primarily produces water vapor (H2O), making it a very clean fuel with minimal environmental pollution compared to fossil fuels.
  • Combustion of fossil fuels (e.g., coal, diesel, kerosene) releases various pollutants:
    • Carbon Dioxide (CO2): A primary greenhouse gas, contributing to global warming.
    • Sulfur Oxides (SOx) and Nitrogen Oxides (NOx): Key precursors to acid rain formation and respiratory issues.
    • Particulate Matter (PM): Causes respiratory problems and reduces visibility.

Fuel Cells: Principles and Applications

  • Fuel Cell: Electrochemical device, converts chemical energy of a fuel (e.g., Hydrogen) and an oxidant (e.g., Oxygen) directly into electrical energy.
  • Principle: Operates like a continuously refuelled battery; fuel and oxidant supplied continuously.
  • Key Components: Anode, cathode, and an electrolyte.
  • Fuel: Typically Hydrogen (H₂). Oxidant: Oxygen (O₂) from air.
  • Reaction at Anode: H₂ → 2H⁺ + 2e⁻ (Hydrogen is oxidized).
  • Reaction at Cathode: O₂ + 4H⁺ + 4e⁻ → 2H₂O (Oxygen is reduced).
  • Overall Reaction (Hydrogen-Oxygen Fuel Cell): 2H₂ + O₂ → 2H₂O + Electrical Energy + Heat.
  • Exhaust Emission (Hydrogen Fuel Cells): Water vapour (H₂O) and heat.
  • Efficiency: High (40-60%), not limited by Carnot cycle.
  • Environmental Impact: Zero emissions at the point of use (if Hydrogen is produced from renewable sources).
  • Applications: Fuel Cell Electric Vehicles (FCEVs), grid power generation, portable power systems, backup power.

Fuel Quality: Octane Number, Cetane Number

  • Octane Number (for Petrol/Gasoline):
  • Measures petrol's quality and resistance to "knocking" or "detonation" in spark-ignition engines.
  • Higher Octane Number = Greater resistance to knocking = Better ability to withstand compression without premature ignition.
  • Lower Octane Number = Less resistance to knocking = Fuel detonates earlier, causing potential engine damage and reduced efficiency.
  • Reference fuels: Iso-octane (assigned 100 octane, high knock resistance) and n-heptane (assigned 0 octane, low knock resistance).
  • Cetane Number (for Diesel):
  • Measures diesel fuel's ignition quality and ignition delay in compression-ignition (diesel) engines.
  • Higher Cetane Number = Shorter ignition delay = Smoother cold starting and better combustion performance.
  • Lower Cetane Number = Longer ignition delay = Rougher engine operation, potential misfires, especially in cold conditions.
  • Reference fuels: n-cetane (assigned 100 cetane, very short ignition delay) and alphamethylnaphthalene (assigned 0 cetane, long ignition delay).
  • Winter Diesel:
  • A specialized diesel fuel designed for use in very low-temperature regions (e.g., down to – 30°C).
  • Contains additives to maintain lower viscosity and prevent gelling/waxing (cloud point, pour point depressants).
  • Has a higher cetane rating for improved cold starting and engine performance.
  • Features low sulfur content.
  • Fuel from Plastic Waste:
  • Fuel obtained from plastic waste (e.g., pyrolysis oil) typically has a low octane rating and often requires significant upgrading/ refining to meet standard gasoline specifications.

Gaseous Fuels: Natural Gas (LPG, CNG), Biogas, Producer Gas, Water Gas, Hydrogen Fuel

  • Natural Gas: Primarily Methane (CH₄), also contains higher hydrocarbons. Known for its high calorific value.
  • CNG (Compressed Natural Gas): Main constituent is Methane (CH₄), often with some Ethane (C₂H₆). Used as a cleaner fuel in automobiles to reduce pollution.
  • LPG (Liquefied Petroleum Gas): Main constituents are Butane (C₄H₁₀) and Propane (C₃H₈). Commonly used as cooking gas.
  • LPG Leakage Detection: Ethyl mercaptan (a sulfur-containing compound) is added to LPG to impart a distinct odor for easy detection of leaks.
  • Biogas: Main constituents are Methane (CH₄, 50-75%) and Carbon Dioxide (CO₂, 25-50%). It is a clean fuel, releasing no smoke or residue. Its higher CO₂ content results in a lower energy (calorific) value compared to natural gas.
  • Water Gas (Syngas/Synthesis Gas): A mixture of Carbon Monoxide (CO) and Hydrogen (H₂). Produced, for example, by the steam reforming of methane: CH₄(g) + H₂O(g) → CO(g) + 3H₂(g). It has a higher calorific value than producer gas.
  • Producer Gas: A mixture of Carbon Monoxide (CO) and Nitrogen (N₂). It has a lower calorific value compared to natural gas and water gas.
  • Clean Fuel Examples: Propane and Biogas.
  • Welding Gases: Oxygen (O₂) and Acetylene (C₂H₂) are commonly used.

Liquid Fuels: Petroleum Refining, Petrol, Diesel, Kerosene, Bio-ethanol, Bio-diesel

  • Petroleum Refining: Crude oil separated into fractions (e.g., petrol, diesel, kerosene) by fractional distillation based on boiling points.
  • Petrol (Gasoline): Lighter fraction, used in spark-ignition internal combustion engines. Octane number indicates anti-knock property.
  • Diesel: Heavier fraction than petrol, used in compression-ignition (diesel) engines. Cetane number indicates ignition quality.
  • Kerosene: Middle distillate fraction. Used as lamp fuel, heating oil, and critically, as jet fuel (Aviation Turbine Fuel - ATF) for turbine-based aviation engines.
  • Bio-ethanol: Alcohol fuel produced by fermentation of biomass (sugarcane, corn, cellulosic materials). Blended with petrol (e.g., E10, E20).
  • Bio-diesel: Fuel produced from vegetable oils or animal fats through transesterification. Blended with conventional diesel.

Rocket Propellants: Chemical Basis and Types

  • Rocket propellants are mass expelled to generate thrust (Newton's 3rd Law).
  • Chemical basis involves highly energetic, exothermic reactions producing hot gases at high velocity.
  • Types of Propellants:
    • Solid Propellants:
      • Simpler design, stable storage, lower specific impulse (Isp).
      • Composition: Fuel, oxidizer, binder.
      • Examples:
      • Composite: Ammonium Perchlorate Composite Propellant (APCP) - Oxidizer: Ammonium Perchlorate (NH₄ClO₄); Fuel: aluminum powder; Binder: polymer (e.g., HTPB).
      • Double-base: Nitrocellulose and Nitroglycerin.
    • Liquid Propellants:
      • Complex systems, allow throttling and restarts, higher specific impulse (Isp).
      • Types:
      • Monopropellants: A single chemical that decomposes catalytically.
      • Example: Hydrazine (N₂H₄) – decomposes into N₂, H₂, NH₃, generating thrust.
      • Bipropellants: Two separate chemicals (fuel + oxidizer) mixed in a combustion chamber.
      • Fuels:
      • Kerosene (RP-1).
      • Liquid Hydrogen (LH₂).
      • Hydrazine (N₂H₄) and its derivatives (e.g., Monomethylhydrazine MMH, Unsymmetrical Dimethylhydrazine UDMH).
      • Oxidizers:
      • Liquid Oxygen (LOX).
      • Nitric Acid (HNO₃).
      • Nitrogen Tetroxide (NTO / N₂O₄).
      • Hydrogen Peroxide (H₂O₂).

Solid Fuels: Coal (types, composition, coking), Wood, Biomass

  • Solid Fuels are organic materials used as energy sources.
  • Coal is a fossil fuel formed from plant matter under heat and pressure over geological time, primarily composed of carbon.
  • Types of Coal (by increasing carbon content/ quality):
    • Peat: First stage, lowest carbon (<60%), highest moisture, lowest heating value, resembles soil.
    • Lignite (Brown Coal): Second stage, carbon 60-70%, high moisture, moderate heating value, used for electricity.
    • Bituminous Coal (Soft Coal): Third stage, carbon 70-85%, most abundant, good heating value, widely used for electricity, cement, and coking.
    • Anthracite (Hard Coal): Highest grade, carbon 85-95%+, lowest volatile matter/moisture, highest calorific value, burns cleanest, least smoke, lustrous. It is considered the best quality coal.
  • Coking: Process of heating specific grades of Bituminous coal in the absence of air (destructive distillation) to produce coke.
  • Coke: A porous, high-carbon fuel (approx. 90% carbon) used mainly in blast furnaces (metallurgy) due to its purity and high heating value.
  • Wood: A traditional solid biomass fuel; renewable, high moisture, lower calorific value than coal, produces more smoke and ash.
  • Biomass: Organic material (e.g., wood, agricultural waste, animal dung) derived from living or recently living organisms, used as fuel; a renewable energy source.

Synthetic Fuels: Basics of Production

  • Synthetic fuels are fuels produced from sources other than conventional crude oil, such as coal, natural gas, biomass, or waste.
  • Coal Liquefaction is the process of converting solid coal into liquid hydrocarbon fuels.
  • Two primary methods for coal liquefaction:
    • Direct Coal Liquefaction (DCL): Coal is directly converted into liquid fuels by hydrogenation under high temperature and pressure, often with a catalyst.
    • Indirect Coal Liquefaction (ICL): Coal is first gasified to produce syngas (a mixture of carbon monoxide (CO) and hydrogen (H₂)), which is then converted into liquid fuels using processes like Fischer-Tropsch synthesis.

18. Food Preservation, Nutrition,

Medicine, etc.

Practice MCQs: The Fuel

Biofuels: First, Second, and Third Generation

  1. Which of the following is not an explosive

    Asked in: ASSISTANT AUDIT OFFICER 2017 18 2017

    1. RDX
    2. TNT
    3. CNG
    4. TNG
    Show answer

    Answer: C. CNG

    Explosives are substances that can undergo rapid chemical decomposition, producing a large volume of gas and heat, resulting in a sudden expansion and shockwave. C. Both the Processes A & B are chemical changes. D. Both the Processes A & B are physical changes. Ans: C Junior Accountant and TRA -2013 Chemical changes involve the formation of new substances with different properties, while physical changes alter the form or appearance but not the chemical composition.

Calorific Value and Fuel Efficiency

  1. Which one of the following has the highest fuel value?

    Asked in: UPPCS Prelims 1997

    1. Hydrogen
    2. Charcoal
    3. Natural Gas
    4. Gasoline
    Show answer

    Answer: A. Hydrogen

    Fuel value (calorific value) is the amount of energy released per unit mass or volume of a fuel when it undergoes complete combustion. Hydrogen has the highest calorific value by mass compared to other common fuels.

  2. Which of the following has maximum calorific energy value ?

    Asked in: Deputy Superintendent of Police (Police Telecom) Exam 2024

    1. Methane
    2. Ethanol
    3. Hydrogen
    4. Butane
    Show answer

    Answer: C. Hydrogen

    Hydrogen's high calorific value makes it a very efficient fuel, though its storage and handling present challenges.

Combustion: Types, Mechanism, and Products

  1. What is a fire triangle ?

    Asked in: UPSC CISF AC EXE 2017

    1. Combination of Oxygen, Fuel and Heat
    2. Combination of Heat, Gas and CO₂
    3. Combination of Fuel, CO₂ and Heat
    4. None of the above
    Show answer

    Answer: A. Combination of Oxygen, Fuel and Heat

    The fire triangle is a simple model illustrating the three elements necessary for most fires to ignite and continue to burn: Fuel (something to burn), Oxygen (a supply of oxidizer, usually air), and Heat (sufficient to raise the fuel to its ignition temperature). Removing any one of these elements can extinguish the fire.

  2. Which one of the following substances does not belong to class 'B' fire ?

    Asked in: UPSC CISF AC EXE 2020

    1. Molten Sulphur
    2. Alcohol
    3. Solvent
    4. Paint
    Show answer

    Answer: D. Paint

    - Class B fires involve flammable liquids and gases (e.g., petrol, oil, alcohol, propane). - Alcohol and Solvents are standard examples of flammable liquids that cause Class B fires. - Molten Sulphur, while solid at room temperature, burns as a flammable liquid when molten and is classified as a Class B fire hazard. - Paint's classification depends on its composition. Solvent-based paints cause Class B fires due to the flammable solvents. However, water-based paints contain minimal flammable solvents; their fire risk is primarily from the combustible solid components/residue, which would be a Class A fire. Dried paint is also a combustible solid (Class A).

Environmental Impact of Fuel Combustion: Pollution, Greenhouse Gases, Acid Rain

  1. Combustion of petrol in automobiles pollute air by producing following metal

    Asked in: CGPSC Prelims Exam 2015

    1. Mercury
    2. Cadmium
    3. Lead
    4. Carbon Dioxide
    Show answer

    Answer: C. Lead

    Historically, petrol contained tetraethyllead (TEL) as an anti-knocking agent to improve engine performance. When this leaded petrol was combusted, lead compounds were emitted into the atmosphere, leading to significant air pollution and health problems. The phasing out of leaded petrol has been a major global effort to reduce lead pollution.

  2. Which of the following fuels would produce minimum environmental pollution?

    Asked in: UPPCS Prelims 2017

    1. Hydrogen
    2. Diesel
    3. Kerosene
    4. Coal
    Show answer

    Answer: A. Hydrogen

    Hydrogen combustion is much cleaner than that of fossil fuels, producing water rather than greenhouse gases and air pollutants.

Fuel Cells: Principles and Applications

  1. Which one of the following is the exhaust pipe emission from Fuel Cell Electric Vehicles, powered by hydrogen ?

    Asked in: UPSC IAS 2024

    1. Hydrogen peroxide
    2. Hydronium
    3. Oxygen
    4. Water vapour
    Show answer

    Answer: D. Water vapour

    The fundamental output of a hydrogen fuel cell, besides electricity and heat, is water.

Fuel Quality: Octane Number, Cetane Number

  1. Consider the following statements and choose the right options given below. (1) Fuel obtained from plastic waste has low octane rating. (2) Lower the octane number, more is the ability of the fuel to withstand compression without detonating.

    Asked in: CGPSC Prelims Exam 2023

    1. Only the statement (1) is correct
    2. Only the statement (2) is correct
    3. Both the statements (1) and (2) are in-correct
    4. Both the statements (1) and (2) are correct
    Show answer

    Answer: A. Only the statement (1) is correct

    Statement (1) is correct: Fuel obtained from plastic waste through processes like pyrolysis often yields a complex mixture of hydrocarbons. The liquid product before extensive refining can have a lower octane rating compared to standard gasoline, although it can be upgraded. Statement (2) is incorrect: Octane number measures a fuel's resistance to knocking or detonation under compression. A higher octane number indicates greater resistance to detonation, allowing the fuel to withstand higher compression ratios before igniting spontaneously.

  2. The quality of diesel oil for use in diesel engines is determined by :

    Asked in: HPPSC HPAS Prelims 2011

    1. The composition of the oil
    2. The octane number
    3. The cetane number
    4. The amount of additives added
    Show answer

    Answer: C. The cetane number

    The cetane number is the primary indicator of diesel fuel quality, measuring its ignition delay.

  3. Winter Diesel is a specialized fuel that was introduced by Indian Oil Corporation. Choose the incorrect statement about Winter Diesel :

    Asked in: PPSC CS Prelims 2021

    1. It contains additives to maintain lower viscos‐ ity so that it can be used in temperatures as low as – 30°C.
    2. It has lower cetane rating for high performance of engines.
    3. It has low Sulphur content to ensure lesser deposition in engines.
    4. It is highly suitable for high altitude and low- temperature regions such as Ladakh, where ordin‐ ary diesel can become unusable.
    Show answer

    Answer: B. It has lower cetane rating for high performance of engines.

    Winter diesel is formulated to prevent gelling at extremely low temperatures and is suitable for high- altitude, cold regions. Like modern fuels, it has low sulfur content. A lower cetane rating would be detrimental to engine performance, especially in cold conditions, so winter diesel does not have a lower cetane rating for high performance; it requires adequate or higher cetane.

  4. Quality of petrol is expressed in

    Asked in: Civil Engg GA 24 2023 CO 1505 2024

    1. gold number
    2. cetane number
    3. methane number
    4. octane number
    Show answer

    Answer: D. octane number

    The octane number is a measure of a fuel's resistance to knocking or pinging in an internal combustion engine. A higher octane number indicates a greater resistance to knocking. Petrol with a higher octane rating is generally used in higher- compression engines.

Gaseous Fuels: Natural Gas (LPG, CNG), Biogas, Producer Gas, Water Gas, Hydrogen Fuel

  1. Gases used in welding are

    Asked in: BPSC Prelims Exam 63rd

    1. oxygen and hydrogen
    2. oxygen and nitrogen
    3. oxygen and acetylene
    4. hydrogen and acetylene
    Show answer

    Answer: C. oxygen and acetylene

    - Oxy-acetylene welding is a process that uses the combustion of acetylene and oxygen to produce a high-temperature flame (around 3,500 °C or 6,330 °F) that melts and joins metals. - Acetylene (C₂H₂) acts as the fuel gas. - Oxygen (O₂) is used as the oxidizer, supporting the combustion and increasing the flame temperature. - Other fuel gases can be used with oxygen (like propane, natural gas), but acetylene is the most common for welding due to its high flame temperature.

  2. Which is main component of natural gas ?

    Asked in: CGPSC Prelims Exam 2016

    1. Methane
    2. Ethane
    3. Propane
    4. Benzene
    Show answer

    Answer: A. Methane

    Methane (CH₄) is the main component of natural gas, typically making up between 70% and 90% of its volume. Other components include smaller amounts of ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀), and other gases like nitrogen and carbon dioxide.

  3. Water gas is

    Asked in: CGPSC Prelims Exam 2016

    1. CO + H2
    2. CO + H2O
    3. CO2 + H2
    4. CO2+H2O
    Show answer

    Answer: A. CO + H2

    It is produced industrially by the reaction of steam with hydrocarbons, such as passing steam over hot coke (carbon) at high temperatures (around 1000 °C): C + H₂O → CO + H₂.

  4. Match the names of the fuels in Column I with their dominant chemical properties given in Column II and select the correct answer using the options given below the columns: Column I Column II 1. Water Gas a. Methane 2. Natural Gas b. Butane and Propane 3. CNG c. Methane, Ethane 4. LPG d. Carbon Monoxide, Hydrogen

    Asked in: HAS Prelims 2019

    1. 1-d, 2-c, 3-a, 4-b
    2. 1-a, 2-d, 3-c, 4-b
    3. 1-b, 2-d, 3-b, 4-a
    4. 1-c, 2-a, 3-b, 4-d
    Show answer

    Answer: A. 1-d, 2-c, 3-a, 4-b

    Let's match the fuels with their dominant chemical properties: 1. Water Gas is a mixture of carbon monoxide (CO) and hydrogen (H₂) gas. This matches option 'd'. 2. Natural Gas primarily consists of methane (CH₄), but typically also contains varying amounts of other higher alkanes like ethane (C₂H₆), propane (C₃H₈), etc. Option 'c' (Methane, Ethane) is a common composition. 3. CNG (Compressed Natural Gas) is predominantly methane (CH₄). This matches option 'a'. 4. LPG (Liquefied Petroleum Gas) is a mixture of propane (C₃H₈) and butane (C₄H₁₀). This matches option 'b'.

  5. Assertion (A) : Biogas contains large amounts of methane which can be used as a fuel for several purposes. As it releases no smoke or residue, it should be considered as a good and safe source of energy. Reason (R) : Biogas also contains carbon dioxide and the higher content of carbon dioxide contributes to lower energy of biogas in comparison to natural gas. In the light of the above statements, choose the most appropriate answer from the options given below:

    Asked in: HAS Prelims 2021

    1. Both (A) and (R) are correct and (R) is the correct explanation of (A)
    2. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
    3. (A) is correct but (R) is not correct
    4. (A) is not correct but (R) is correct
    Show answer

    Answer: B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)

    Assertion (A) states that biogas contains large amounts of methane (the primary combustible component, typically 50-75%) and can be used as fuel, and that it's a good and safe source due to releasing no smoke or residue (relatively clean combustion compared to some fuels). This statement is largely correct. Reason (R) states that biogas also contains carbon dioxide (typically 25-50%) and this higher CO2 content contributes to lower energy content (calorific value) compared to natural gas (which is mostly methane). This statement is also correct. However, Reason (R) explains a characteristic of biogas (lower energy density due to CO2) compared to natural gas; it does not explain why biogas is considered a good and safe source of energy, which is related to its methane content and cleaner burning properties mentioned in Assertion (A).

  6. Cooking gas is a mixture of

    Asked in: JPSC CS Prelims 2011

    1. carbon monoxide and carbon dioxide
    2. butane and propane
    3. methane and ethylene
    4. carbon dioxide and oxygen
    Show answer

    Answer: B. butane and propane

    - LPG is a flammable mixture of hydrocarbon gases used as fuel in heating appliances, vehicles, and increasingly, as an aerosol propellant and a refrigerant. - The exact proportion of propane and butane can vary depending on the source and the season (propane is favored in colder climates due to its lower boiling point).

  7. Which one of the following is water gas ?

    Asked in: UPSC NDA 1 2016

    1. Mixture of carbon monoxide and hydrogen
    2. Mixture of carbon monoxide and nitrogen
    3. Mixture of carbon dioxide and water vapour
    4. Mixture of carbon monoxide and water vapour
    Show answer

    Answer: A. Mixture of carbon monoxide and hydrogen

    Water gas is a synthesis gas mixture primarily consisting of carbon monoxide (CO) and hydrogen (H₂). It is produced by passing steam over hot carbon (like coke or coal) at high temperatures (typically 700-1000 °C). The reaction is C + H₂O → CO + H₂.

  8. Which one of the following is an example of a clean fuel ?

    Asked in: UPSC NDA 1 2019

    1. Coke
    2. Propane
    3. Petrol
    4. Wax
    Show answer

    Answer: B. Propane

    Clean fuels produce less pollution when burned compared to conventional fuels. Propane, being a gaseous fuel (part of LPG - Liquefied Petroleum Gas), generally burns more cleanly than solid fuels like coke or liquid fuels like petrol and wax, which produce significant amounts of smoke, particulate matter, and other pollutants like sulfur oxides and nitrogen oxides. While no fuel is perfectly "clean," propane is significantly cleaner than the other options listed in terms of common air pollutants.

  9. Water gas is a mixture of:

    Asked in: UPSC NDA 1 2024

    1. CO₂ and H₂
    2. CO and H₂
    3. CO₂ and H₂O
    4. CO and H₂O
    Show answer

    Answer: B. CO and H₂

    It is produced by passing steam over red-hot carbon (like coke or coal) at high temperatures (typically 800-1000°C). The reaction is: H₂O(g) + C(s) → CO(g) + H₂(g).

Liquid Fuels: Petroleum Refining, Petrol, Diesel, Kerosene, Bio-ethanol, Bio-diesel

  1. Jet fuel used in turbine based aviation engine mainly consists of

    Asked in: OPSC CS Prelims 2022

    1. Petrol
    2. Diesel
    3. Kerosene
    4. CNG
    Show answer

    Answer: C. Kerosene

    Jet fuel (like Jet A or Jet A-1), used in turbine aviation engines, is a refined form of kerosene. It is engineered to meet the specific requirements for aircraft operation, such as high energy density and performance at varying altitudes and temperatures.

Rocket Propellants: Chemical Basis and Types

  1. The compound is used as rocket propellant

    Asked in: TNPSC CS Prelims 2014

    1. Hydrazine
    2. Nitric acid
    3. Ammonia
    4. Nitrogen
    Show answer

    Answer: A. Hydrazine

    Hydrazine and its derivatives (like monomethylhydrazine - MMH, and unsymmetrical dimethylhydrazine - UDMH) are common components of rocket fuels due to their high energy density and ability to undergo rapid exothermic decomposition.

Solid Fuels: Coal (types, composition, coking), Wood, Biomass

  1. The best quality coal is

    Asked in: WBCS Main Paper 4 2023

    1. Anthracite
    2. Peat
    3. Bituminous
    4. Lignite
    Show answer

    Answer: A. Anthracite

    Coal quality is primarily determined by its carbon content and energy density. Anthracite is the highest rank of coal, containing the highest proportion of fixed carbon (typically >86%) and providing the most heat energy when burned.

Synthetic Fuels: Basics of Production

  1. The process that converts solid coal into liquid hydrocarbon fuel is called ________.

    Asked in: GPSC Prelims CSP 2 2019

    1. Liquefaction
    2. Carbonation
    3. Catalytic conversion
    4. Cracking
    Show answer

    Answer: A. Liquefaction

    Coal liquefaction is a process of converting coal into liquid hydrocarbons: methanol (indirect liquefaction) or synthetic fuels (direct liquefaction). This can be done through various chemical processes, typically involving heat, pressure, and catalysts. Bromides, particularly potassium bromide, were widely used in medicine in the late 19th and early 20th centuries as sedatives and for treating epilepsy. Although largely replaced by newer drugs today, they are still sometimes used in veterinary medicine. Bromide ions depress the central nervous system.

  2. Who established the structure of Penicillin by X-ray analysis ?

    Asked in: DENTAL SURGEON (SCREENING) EXAMINATION 2023

    1. Alexander Flemming
    2. Pasteur Joubert
    3. Robert Koch
    4. Dorothy Hodgkin
    Show answer

    Answer: D. Dorothy Hodgkin

    The question asks to identify the scientist who established the structure of Penicillin using X-ray analysis. This requires knowledge of significant figures in scientific discovery and their specific contributions.

  3. Which of the following antibiotic drug was discovered by Alexander Fleming ?

    Asked in: Co operative Supervisor & Environment Supervisor (Group C) Exam 2023

    1. Ofloxacin
    2. Tetracycline
    3. Penicillin
    4. None of these
    Show answer

    Answer: C. Penicillin

    Alexander Fleming's discovery of penicillin revolutionized medicine by providing a treatment for bacterial infections, saving countless lives.