📌 How to Use
Select Read to study MCQs carefully. Select Practice Quiz to test yourself.
📘 Study MCQs
Q1. The part of a candle flame that is the hottest and appears blue is the: NCERT 2023
• Innermost zone
• Middle zone
• Outermost zone
• Wick
Answer: Outermost zone
The outermost zone is where complete combustion takes place, making it the hottest part of the flame.
It appears blue in color.
Q2. The middle zone of a candle flame is yellow because it contains: NCERT 2023
• Fully burnt wax vapors
• Unburnt carbon particles that glow
• Oxygen gas
• Water vapor
Answer: Unburnt carbon particles that glow
Incomplete combustion in the middle zone produces tiny carbon particles that get heated and emit yellow light, making the zone luminous.
Q3. The innermost zone of a candle flame consists of: NCERT 2023
• Hot burnt gases
• Unburnt wax vapors
• Carbon dioxide
• Oxygen
Answer: Unburnt wax vapors
The innermost zone is the coolest part of the flame and contains unburnt wax vapors that have not yet started burning.
Q4. A substance that burns in air to produce heat and light is called a: NCERT 2023
• Fire extinguisher
• Fuel
• Supporter of combustion
• Inflammable substance
Answer: Fuel
A fuel is any substance that undergoes combustion to release energy in the form of heat and light.
Q5. The efficiency of a fuel is determined by its: NCERT 2023
• Color
• Cost
• Calorific value
• Ignition temperature
Answer: Calorific value
Calorific value is the amount of heat energy produced by complete combustion of one kilogram of a fuel, indicating its efficiency.
Q6. The unit in which calorific value of a fuel is expressed is: NCERT 2023
• Kilogram
• Liter
• Kilojoule per kilogram (kJ/kg)
• Degree Celsius
Answer: Kilojoule per kilogram (kJ/kg)
Calorific value is measured in kilojoules per kilogram, representing the heat energy released per unit mass of the fuel.
Q7. Which of the following fuels has the highest calorific value? NCERT 2023
• Wood
• Cow dung cakes
• Hydrogen
• Kerosene
Answer: Hydrogen
Hydrogen has the highest calorific value of around 150,000 kJ/kg, making it a highly efficient fuel, though it is not commonly used due to safety concerns.
Q8. The calorific value of a fuel is defined as: NCERT 2023
• The temperature at which it catches fire
• The amount of heat produced by complete combustion of 1 kg of fuel
• The amount of oxygen needed for combustion
• The ash content left after burning
Answer: The amount of heat produced by complete combustion of 1 kg of fuel
Calorific value is a measure of the energy content of a fuel and helps compare the efficiency of different fuels.
Q9. Which of the following fuels produces the least amount of smoke and is considered clean? NCERT 2023
• Coal
• Wood
• Cow dung cakes
• CNG
Answer: CNG
Compressed Natural Gas (CNG) burns completely and produces very little smoke or harmful gases, making it a clean fuel.
Q10. Burning of fuels like coal and wood releases which harmful gas that can cause respiratory problems? NCERT 2023
• Oxygen
• Nitrogen
• Carbon monoxide
• Hydrogen
Answer: Carbon monoxide
Incomplete combustion of fuels releases carbon monoxide, which is a poisonous gas that can cause serious health issues when inhaled.
Q11. The gas released by burning fuels that is mainly responsible for global warming is: NCERT 2023
• Oxygen
• Nitrogen
• Carbon dioxide
• Hydrogen
Answer: Carbon dioxide
Carbon dioxide is a greenhouse gas that traps heat in the atmosphere, leading to an increase in Earth’s average temperature, known as global warming.
Q12. The phenomenon of increase in Earth’s average temperature due to excessive release of greenhouse gases is called: NCERT 2023
• Acid rain
• Global warming
• Ozone depletion
• Deforestation
Answer: Global warming
Global warming is caused by the buildup of greenhouse gases like carbon dioxide, methane, and nitrous oxide from burning fuels and other human activities.
Q13. Acid rain is caused mainly by the presence of which gases in the atmosphere? NCERT 2023
• Oxygen and hydrogen
• Nitrogen oxides and sulfur dioxide
• Carbon monoxide and ozone
• Water vapor and methane
Answer: Nitrogen oxides and sulfur dioxide
When fuels containing sulfur and nitrogen are burned, they release sulfur dioxide and nitrogen oxides. These gases dissolve in rainwater to form acids.
Q14. Acid rain can damage: NCERT 2023
• Buildings and monuments
• Soil and water bodies
• Forests and crops
• All of the above
Answer: All of the above
Acid rain corrodes buildings, especially those made of marble, harms aquatic life, damages soil quality, and affects plant growth.
Q15. The full form of CNG is: NCERT 2023
• Compressed Natural Gas
• Carbon Nitrogen Gas
• Combined Natural Gas
• Compressed Nitrogen Gas
Answer: Compressed Natural Gas
CNG stands for Compressed Natural Gas, which is stored at high pressure and used as a fuel in vehicles and for other purposes.
Q16. Which of the following is an ideal fuel? NCERT 2023
• One that has low calorific value and produces lot of smoke
• One that is expensive and difficult to store
• One that has high calorific value, burns without smoke, and is easy to handle
• One that has high ignition temperature and leaves large amount of ash
Answer: One that has high calorific value, burns without smoke, and is easy to handle
An ideal fuel should have high calorific value, be readily available, burn without releasing harmful substances, and be easy to transport and store.
Q17. Inflammable substances are those which have: NCERT 2023
• High ignition temperature
• Very low ignition temperature
• No ignition temperature
• High calorific value
Answer: Very low ignition temperature
Inflammable substances, such as petrol, alcohol, and LPG, catch fire very easily because their ignition temperature is low.
Q18. Which of the following is an inflammable substance? NCERT 2023
• Water
• Stone
• Petrol
• Iron rod
Answer: Petrol
Petrol has a very low ignition temperature and catches fire easily, making it an inflammable substance. It should be stored with care.
Q19. The device used to extinguish fires is called a: NCERT 2023
• Fire starter
• Fire extinguisher
• Fuel injector
• Combustion chamber
Answer: Fire extinguisher
A fire extinguisher is a device that contains materials to put out fires by cutting off oxygen supply, cooling the fuel, or removing heat.
Q20. The most common type of fire extinguisher used for electrical fires contains: NCERT 2023
• Water
• Sand
• Carbon dioxide
• Petrol
Answer: Carbon dioxide
Carbon dioxide does not conduct electricity and cuts off oxygen supply, making it safe and effective for electrical fires.
Q21. CNG is preferred over petrol and diesel in vehicles because it: NCERT 2023
• Produces more smoke
• Is more expensive
• Causes less pollution and is cleaner
• Has lower calorific value
Answer: Causes less pollution and is cleaner
CNG burns more completely than petrol or diesel, producing fewer harmful emissions like carbon monoxide and particulate matter.
Q22. The process of cutting down trees on a large scale is called: NCERT 2023
• Reforestation
• Afforestation
• Deforestation
• Conservation
Answer: Deforestation
Deforestation is the removal of forests for agriculture, urbanization, or other purposes, which contributes to global warming and environmental imbalance.
Q23. Which of the following is a consequence of deforestation? NCERT 2023
• Increase in oxygen levels
• Decrease in carbon dioxide levels
• Increase in global warming
• Reduction in soil erosion
Answer: Increase in global warming
Trees absorb carbon dioxide. Deforestation reduces this absorption, leading to higher carbon dioxide levels in the atmosphere, which contributes to global warming.
Q24. A sudden reaction that releases a large amount of heat, light, gas, and sound is called an: NCERT 2023
• Explosion
• Rapid combustion
• Slow combustion
• Spontaneous combustion
Answer: Explosion
An explosion is a violent form of combustion that occurs suddenly, like in firecrackers or when a gas leak ignites.
Q25. Which of the following fuels is considered a renewable source of energy? NCERT 2023
• Coal
• Natural gas
• Wood (if sourced from sustainable forests)
• Diesel
Answer: Wood (if sourced from sustainable forests)
Wood can be a renewable fuel if trees are replanted at the same rate they are cut. However, fossil fuels like coal and diesel are non-renewable.
Q26. The green color of a flame indicates: NCERT 2023
• Incomplete combustion
• Complete combustion
• Presence of copper compounds
• Presence of carbon particles
Answer: Complete combustion
A blue or greenish flame generally indicates complete combustion with sufficient oxygen supply, producing more heat and less smoke.
Q27. The black smoke produced by burning fuels like coal and diesel is due to: NCERT 2023
• Complete combustion
• Incomplete combustion
• High calorific value
• Low ignition temperature
Answer: Incomplete combustion
Incomplete combustion occurs when there is insufficient oxygen, leading to the formation of unburnt carbon particles that appear as black smoke.
Q28. Which of the following is a harmful substance released by burning of fuels that causes acid rain? NCERT 2023
• Carbon dioxide
• Oxygen
• Sulfur dioxide
• Water vapor
Answer: Sulfur dioxide
Sulfur dioxide is released when fuels containing sulfur are burned. It reacts with water vapor in the atmosphere to form sulfuric acid, a component of acid rain.
Q29. The calorific value of wood is approximately: NCERT 2023
• 17,000 to 22,000 kJ/kg
• 45,000 kJ/kg
• 150,000 kJ/kg
• 1,000 kJ/kg
Answer: 17,000 to 22,000 kJ/kg
Wood has a moderate calorific value, typically ranging between 17,000 and 22,000 kJ/kg, which is lower than that of fossil fuels.
Q30. An ideal fuel should have: NCERT 2023
• High ash content
• Low calorific value
• Moderate to high calorific value and low pollution
• Very high ignition temperature
Answer: Moderate to high calorific value and low pollution
An ideal fuel balances high energy output with minimal environmental impact and ease of use.
Q31. The substance in a fire extinguisher that helps cool the burning material is: NCERT 2023
• Carbon dioxide
• Water
• Nitrogen
• Oxygen
Answer: Water
Water absorbs heat from the burning material, lowering its temperature below the ignition point, and also helps cut off oxygen.
Q32. Which of the following is a major contributor to global warming? NCERT 2023
• Planting trees
• Using solar energy
• Burning of fossil fuels
• Using CNG in vehicles
Answer: Burning of fossil fuels
Burning fossil fuels like coal, oil, and natural gas releases large amounts of carbon dioxide, a greenhouse gas that traps heat and causes global warming.
Q33. LPG is a mixture of: NCERT 2023
• Methane and ethane
• Propane and butane
• Hydrogen and oxygen
• Carbon dioxide and nitrogen
Answer: Propane and butane
Liquefied Petroleum Gas (LPG) is primarily composed of propane and butane, which are stored in liquid form under pressure.
Q34. Which of the following statements about CNG is correct? NCERT 2023
• It is more polluting than petrol
• It is stored in liquid form
• It is a clean-burning fuel
• It has a very low calorific value
Answer: It is a clean-burning fuel
CNG produces fewer harmful emissions compared to petrol and diesel, making it an environmentally friendly fuel for vehicles.
Q35. The release of harmful substances into the environment from burning fuels can cause: NCERT 2023
• Respiratory diseases
• Damage to buildings
• Climate change
• All of the above
Answer: All of the above
Burning fuels releases pollutants that affect human health, damage structures through acid rain, and contribute to climate change.
Q36. Which of the following is an example of an explosion? NCERT 2023
• Burning of a candle
• Rusting of iron
• Bursting of a firecracker
• Burning of wood in a stove
Answer: Bursting of a firecracker
An explosion involves a sudden, violent release of energy with high heat, light, gas, and sound, as seen in a firecracker.
Q37. The outermost zone of a candle flame is also called the: NCERT 2023
• Zone of incomplete combustion
• Zone of complete combustion
• Dark zone
• Luminous zone
Answer: Zone of complete combustion
In this zone, wax vapors burn completely with sufficient oxygen, producing the highest temperature and a blue flame.
Q38. Which fuel has a calorific value of about 45,000 kJ/kg and is commonly used in vehicles? NCERT 2023
• Wood
• Cow dung
• Petrol or diesel
• Hydrogen
Answer: Petrol or diesel
Petrol and diesel have calorific values around 45,000 kJ/kg, making them efficient fuels for transportation.
Q39. The phenomenon of acid rain can be reduced by: NCERT 2023
• Burning more coal
• Using more diesel vehicles
• Using cleaner fuels like CNG
• Cutting down more forests
Answer: Using cleaner fuels like CNG
Cleaner fuels produce fewer sulfur dioxide and nitrogen oxides, reducing the formation of acids in rainwater.
Q40. Which of the following is not a characteristic of an ideal fuel? NCERT 2023
• Easy to store and transport
• Leaves no residue after burning
• Has a very high ignition temperature
• Burns without producing smoke
Answer: Has a very high ignition temperature
An ideal fuel should have a moderate ignition temperature so it can be ignited easily but is not dangerously inflammable.
Q41. The gas used in fire extinguishers that works by cutting off oxygen supply is: NCERT 2023
• Oxygen
• Hydrogen
• Carbon dioxide
• Nitrogen dioxide
Answer: Carbon dioxide
Carbon dioxide is heavier than air and forms a layer over the burning material, preventing oxygen from reaching it.
Q42. Incomplete combustion of fuels produces: NCERT 2023
• Only carbon dioxide and water
• Carbon monoxide, carbon particles, and unburnt hydrocarbons
• Only nitrogen and oxygen
• Only sulfur dioxide
Answer: Carbon monoxide, carbon particles, and unburnt hydrocarbons
When oxygen supply is insufficient, fuels do not burn completely, producing harmful substances like carbon monoxide and soot.
Q43. Which of the following is a way to reduce global warming? NCERT 2023
• Increase use of fossil fuels
• Cut down more forests
• Use renewable energy sources like solar and wind power
• Burn more coal
Answer: Use renewable energy sources like solar and wind power
Renewable energy sources do not release carbon dioxide, helping to reduce greenhouse gas emissions and slow global warming.
Q44. The calorific value of a fuel is measured using an instrument called a: NCERT 2023
• Thermometer
• Calorimeter
• Barometer
• Hygrometer
Answer: Calorimeter
A calorimeter is a device used to measure the heat released during the combustion of a fuel to determine its calorific value.
Q45. Which of the following fuels has the lowest calorific value? NCERT 2023
• Hydrogen
• Petrol
• Cow dung cakes
• Natural gas
Answer: Cow dung cakes
Cow dung cakes have a relatively low calorific value, typically between 6,000 and 8,000 kJ/kg, and produce a lot of smoke.
Q46. The color of a flame indicates: NCERT 2023
• The amount of fuel left
• The completeness of combustion
• The weight of the fuel
• The color of the fuel
Answer: The completeness of combustion
A blue flame indicates complete combustion with sufficient oxygen, while a yellow or smoky flame indicates incomplete combustion.
Q47. Which of the following is an example of a non-renewable fuel? NCERT 2023
• Wind energy
• Solar energy
• Coal
• Biomass
Answer: Coal
Coal is a fossil fuel that takes millions of years to form and cannot be replenished quickly, making it a non-renewable resource.
Q48. Acid rain can cause damage to historical monuments like the Taj Mahal because it: NCERT 2023
• Adds color to the marble
• Reacts with marble (calcium carbonate) and corrodes it
• Makes the marble stronger
• Cleans the marble surface
Answer: Reacts with marble (calcium carbonate) and corrodes it
Acid rain contains acids that react with calcium carbonate in marble, causing discoloration and erosion, which damages monuments.
Q49. Inflammable substances should be stored: NCERT 2023
• Near a gas stove
• In direct sunlight
• In cool, well-ventilated areas away from fire sources
• In plastic bags
Answer: In cool, well-ventilated areas away from fire sources
Inflammable substances catch fire easily, so they must be stored safely away from heat sources and in ventilated areas to prevent accumulation of vapors.
Q50. The structure of a candle flame consists of three zones. The correct order from innermost to outermost is: NCERT 2023
• Luminous zone, non-luminous zone, dark zone
• Dark zone, luminous zone, non-luminous zone
• Non-luminous zone, luminous zone, dark zone
• Dark zone, non-luminous zone, luminous zone
Answer: Dark zone, luminous zone, non-luminous zone
The innermost dark zone contains unburnt wax vapors, the middle luminous zone has burning carbon particles, and the outermost non-luminous zone is where complete combustion occurs.