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Q1. The part of a candle flame that is the hottest and appears blue is the:
The outermost zone of a candle flame is the hottest part and appears blue. This is the zone of complete combustion where there is enough oxygen for the wax to burn completely, producing the highest temperature. The innermost zone is dark and cool, the middle zone is yellow and luminous, and the wick provides the fuel.
Q2. The middle zone of a candle flame is yellow because it contains:
The middle zone of a candle flame is yellow and luminous because it contains unburnt carbon particles. These tiny carbon particles get heated to a high temperature and glow, giving the flame its yellow color. This zone has incomplete combustion due to limited oxygen.
Q3. The innermost zone of a candle flame consists of:
The innermost zone of a candle flame is the dark zone near the wick. It contains unburnt wax vapors that have not yet undergone combustion. This zone is the coolest part of the flame and does not have enough oxygen for burning. The wax vapors rise and then burn in the upper zones.
Q4. A substance that burns in air to produce heat and light is called a:
A fuel is a substance that burns in air to produce heat and light. Examples include wood, coal, petrol, and LPG. Fire extinguishers are used to put out fires, supporters of combustion help fire burn, and inflammable substances catch fire easily.
Q5. The efficiency of a fuel is determined by its:
The efficiency of a fuel is determined by its calorific value, which is the amount of heat produced by complete combustion of 1 kg of fuel. A higher calorific value means better efficiency. Color, cost, and ignition temperature are not measures of efficiency.
Q6. The unit in which calorific value of a fuel is expressed is:
The calorific value of a fuel is expressed in kilojoules per kilogram (kJ/kg). This unit measures the amount of heat energy released when 1 kilogram of fuel is completely burned. Kilogram is for mass, liter is for volume, and degree Celsius is for temperature.
Q7. Which of the following fuels has the highest calorific value?
Hydrogen has the highest calorific value among the given fuels (about 150,000 kJ/kg). It is a clean fuel but difficult to store and transport. Wood, cow dung cakes, and kerosene have lower calorific values. Hydrogen produces water when burned, making it environmentally friendly.
Q8. The calorific value of a fuel is defined as:
The calorific value of a fuel is the amount of heat energy released when 1 kilogram of fuel undergoes complete combustion. It is measured in kJ/kg. Ignition temperature is the catching point, oxygen requirement is for combustion, and ash content is the residue.
Q9. Which of the following fuels produces the least amount of smoke and is considered clean?
CNG (Compressed Natural Gas) is considered a clean fuel because it burns completely and produces very little smoke and harmful gases. Coal, wood, and cow dung cakes produce more smoke and pollutants. CNG is widely used as a vehicle fuel to reduce air pollution.
Q10. Burning of fuels like coal and wood releases which harmful gas that can cause respiratory problems?
Carbon monoxide is a harmful gas released by incomplete combustion of fuels like coal and wood. It is poisonous and can cause respiratory problems, headaches, and even death. Oxygen is essential for life, nitrogen is neutral, and hydrogen is a fuel.
Q11. The gas released by burning fuels that is mainly responsible for global warming is:
Carbon dioxide is a greenhouse gas released by burning fuels. It traps heat in the atmosphere and contributes to global warming. Oxygen, nitrogen, and hydrogen are not greenhouse gases. Reducing CO₂ emissions is crucial to combating climate change.
Q12. The phenomenon of increase in Earth’s average temperature due to excessive release of greenhouse gases is called:
Global warming is the increase in Earth’s average temperature caused by excessive release of greenhouse gases like carbon dioxide, methane, and nitrous oxide. Acid rain is caused by sulfur dioxide and nitrogen oxides, ozone depletion is caused by CFCs, and deforestation is cutting down trees.
Q13. Acid rain is caused mainly by the presence of which gases in the atmosphere?
Acid rain is caused by nitrogen oxides and sulfur dioxide released from burning fossil fuels. These gases react with water vapor in the atmosphere to form nitric and sulfuric acids, which fall as acid rain. Oxygen, hydrogen, carbon monoxide, ozone, water vapor, and methane are not the main causes.
Q14. Acid rain can damage:
Acid rain can damage buildings and monuments (especially those made of marble and limestone), soil and water bodies (making them acidic and harming aquatic life), and forests and crops (by damaging leaves and reducing growth). It has widespread harmful effects on the environment.
Q15. The full form of CNG is:
CNG stands for Compressed Natural Gas. It is natural gas stored under high pressure for use as a fuel. It is used in vehicles as a cleaner alternative to petrol and diesel. It is not carbon nitrogen gas, combined natural gas, or compressed nitrogen gas.
Q16. Which of the following is an ideal fuel?
An ideal fuel should have high calorific value (produce more heat), burn without smoke (less pollution), and be easy to handle, store, and transport. It should also have a moderate ignition temperature and leave no residue. This is why LPG and CNG are considered good fuels.
Q17. Inflammable substances are those which have:
Inflammable substances have a very low ignition temperature, meaning they catch fire easily with minimal heat. Petrol, alcohol, and LPG are examples. High ignition temperature means a substance is harder to ignite, and all substances have some ignition temperature.
Q18. Which of the following is an inflammable substance?
Petrol is an inflammable substance with a very low ignition temperature, so it catches fire easily. Water, stone, and iron rods are non-combustible or have high ignition temperatures. Inflammable substances must be handled with care and stored away from fire sources.
Q19. The device used to extinguish fires is called a:
A fire extinguisher is a device used to put out fires. It works by cutting off the oxygen supply, cooling the burning material, or removing the fuel. Fire starters ignite fires, fuel injectors are used in engines, and combustion chambers are where fuel burns.
Q20. The most common type of fire extinguisher used for electrical fires contains:
Carbon dioxide fire extinguishers are used for electrical fires because CO₂ does not conduct electricity and cuts off the oxygen supply. Water should never be used on electrical fires as it conducts electricity and can cause shock. Sand can also be used, but CO₂ is more common.
Q21. CNG is preferred over petrol and diesel in vehicles because it:
CNG is preferred over petrol and diesel because it burns more completely and produces fewer pollutants like carbon monoxide, nitrogen oxides, and particulate matter. It is a cleaner fuel that helps reduce air pollution. It is also cheaper in many places.
Q22. The process of cutting down trees on a large scale is called:
Deforestation is the large-scale cutting down of trees and clearing of forests. Reforestation is planting trees in deforested areas, afforestation is planting trees in new areas, and conservation is protecting natural resources.
Q23. Which of the following is a consequence of deforestation?
Deforestation leads to an increase in global warming because trees absorb carbon dioxide (a greenhouse gas) during photosynthesis. Fewer trees mean more CO₂ in the atmosphere, contributing to global warming. It also increases soil erosion and reduces biodiversity.
Q24. A sudden reaction that releases a large amount of heat, light, gas, and sound is called an:
An explosion is a sudden reaction that releases a large amount of heat, light, gas, and sound. It occurs when combustion happens extremely rapidly. Rapid combustion is fast but not necessarily explosive, slow combustion is gradual, and spontaneous combustion occurs without external ignition.
Q25. Which of the following fuels is considered a renewable source of energy?
Wood is considered a renewable source of energy if it is sourced from sustainably managed forests where trees are replanted. Coal, natural gas, and diesel are fossil fuels and non-renewable. Renewable energy sources can be replenished over time.
Q26. The green color of a flame indicates:
A green flame indicates the presence of copper compounds, which produce a characteristic green color when heated. Complete combustion produces a blue flame, incomplete combustion produces yellow, and carbon particles produce a yellow-orange glow. The green color is due to specific metals.
Q27. The black smoke produced by burning fuels like coal and diesel is due to:
Black smoke is produced by incomplete combustion when there is not enough oxygen. Unburnt carbon particles (soot) are released, forming black smoke. Complete combustion would produce a clean, blue flame with no smoke. High calorific value and low ignition temperature are not causes.
Q28. Which of the following is a harmful substance released by burning of fuels that causes acid rain?
Sulfur dioxide is released by burning fuels containing sulfur (like coal and some diesel). It reacts with water vapor in the atmosphere to form sulfuric acid, which falls as acid rain. Carbon dioxide causes global warming, oxygen is harmless, and water vapor is not harmful.
Q29. The calorific value of wood is approximately:
The calorific value of wood is approximately 17,000 to 22,000 kJ/kg. This is lower than that of fossil fuels like petrol (about 45,000 kJ/kg) and hydrogen (150,000 kJ/kg). Wood has a moderate calorific value and is a traditional fuel.
Q30. An ideal fuel should have:
An ideal fuel should have a moderate to high calorific value (to produce good heat) and cause low pollution (burn without smoke). It should be easy to handle, store, and transport. High ash content, low calorific value, and very high ignition temperature are not desirable.
Q31. The substance in a fire extinguisher that helps cool the burning material is:
Water is the substance in a fire extinguisher that helps cool the burning material. It absorbs heat and lowers the temperature below the ignition point. Carbon dioxide cuts off oxygen, nitrogen is used in some extinguishers, and oxygen supports combustion.
Q32. Which of the following is a major contributor to global warming?
Burning fossil fuels releases large amounts of carbon dioxide, a greenhouse gas that traps heat and contributes to global warming. Planting trees and using solar energy help reduce global warming, and CNG is a cleaner fuel that produces less CO₂.
Q33. LPG is a mixture of:
LPG (Liquefied Petroleum Gas) is a mixture of propane and butane gases. It is stored in liquid form under pressure and is used as a cooking fuel. Methane is the main component of natural gas (CNG). Hydrogen and oxygen are not mixed in LPG.
Q34. Which of the following statements about CNG is correct?
CNG is a clean-burning fuel that produces fewer pollutants than petrol and diesel. It is stored as a compressed gas (not liquid), has a high calorific value, and is less polluting. It is widely used as an alternative fuel for vehicles.
Q35. The release of harmful substances into the environment from burning fuels can cause:
Burning fuels releases harmful substances like carbon monoxide, sulfur dioxide, and carbon dioxide. These can cause respiratory diseases (from pollution), damage buildings (from acid rain), and climate change (from greenhouse gases). All these effects are serious environmental and health concerns.
Q36. Which of the following is an example of an explosion?
Bursting of a firecracker is an example of an explosion, where a sudden reaction releases a large amount of heat, light, gas, and sound. Burning a candle and wood are examples of rapid combustion, and rusting is slow combustion.
Q37. The outermost zone of a candle flame is also called the:
The outermost zone of a candle flame is the zone of complete combustion. It is blue in color and has the highest temperature. The middle zone is the luminous zone with incomplete combustion, and the innermost zone is the dark zone containing unburnt wax vapors.
Q38. Which fuel has a calorific value of about 45,000 kJ/kg and is commonly used in vehicles?
Petrol and diesel have a calorific value of about 45,000 kJ/kg. They are widely used as fuels in vehicles. Wood and cow dung have lower calorific values, and hydrogen has a much higher calorific value but is not commonly used in vehicles.
Q39. The phenomenon of acid rain can be reduced by:
Acid rain can be reduced by using cleaner fuels like CNG, which produce fewer sulfur dioxide and nitrogen oxides. Burning more coal and diesel increases acid rain, and cutting down forests worsens environmental problems. Using cleaner energy sources is key to reducing acid rain.
Q40. Which of the following is not a characteristic of an ideal fuel?
An ideal fuel should not have a very high ignition temperature because it would be difficult to ignite. It should be easy to store, transport, burn without smoke, and leave no residue. A moderate ignition temperature is ideal for practical use.
Q41. The gas used in fire extinguishers that works by cutting off oxygen supply is:
Carbon dioxide is used in fire extinguishers to cut off the oxygen supply and extinguish fires. It is heavier than air and forms a blanket over the burning material, preventing oxygen from reaching it. Oxygen supports combustion, hydrogen is flammable, and nitrogen dioxide is not used.
Q42. Incomplete combustion of fuels produces:
Incomplete combustion produces carbon monoxide (a poisonous gas), carbon particles (soot), and unburnt hydrocarbons. Complete combustion produces only carbon dioxide and water. Nitrogen, oxygen, and sulfur dioxide are not products of incomplete combustion.
Q43. Which of the following is a way to reduce global warming?
Using renewable energy sources like solar and wind power reduces the burning of fossil fuels, decreasing CO₂ emissions and helping to reduce global warming. Increasing fossil fuel use, cutting down forests, and burning more coal would worsen global warming.
Q44. The calorific value of a fuel is measured using an instrument called a:
A calorimeter is an instrument used to measure the calorific value of a fuel. It measures the heat released during complete combustion of a fuel sample. A thermometer measures temperature, a barometer measures atmospheric pressure, and a hygrometer measures humidity.
Q45. Which of the following fuels has the lowest calorific value?
Cow dung cakes have the lowest calorific value among the given fuels (about 6,000-8,000 kJ/kg). Hydrogen has the highest (150,000 kJ/kg), petrol is about 45,000 kJ/kg, and natural gas is about 50,000 kJ/kg. Cow dung is a low-grade fuel.
Q46. The color of a flame indicates:
The color of a flame indicates the completeness of combustion. A blue flame indicates complete combustion, while a yellow or orange flame indicates incomplete combustion with glowing carbon particles. The amount of fuel left, weight, and original color of fuel are not indicated by flame color.
Q47. Which of the following is an example of a non-renewable fuel?
Coal is a non-renewable fuel because it takes millions of years to form and cannot be replenished quickly. Wind energy and solar energy are renewable, and biomass is renewable if managed sustainably. Fossil fuels like coal, petroleum, and natural gas are non-renewable.
Q48. Acid rain can cause damage to historical monuments like the Taj Mahal because it:
Acid rain damages marble (calcium carbonate) by reacting with it to form soluble compounds that wash away. This causes corrosion and discoloration of monuments like the Taj Mahal. It does not add color, make it stronger, or clean it. This is why acid rain is a threat to cultural heritage.
Q49. Inflammable substances should be stored:
Inflammable substances should be stored in cool, well-ventilated areas away from fire sources to prevent accidental fires. Storing them near a gas stove, in direct sunlight, or in plastic bags increases the risk of fire. Proper storage is essential for safety.
Q50. The structure of a candle flame consists of three zones. The correct order from innermost to outermost is:
The correct order of zones in a candle flame from innermost to outermost is: (1) Dark zone (innermost, containing unburnt wax vapors), (2) Luminous zone (middle, yellow, incomplete combustion), and (3) Non-luminous zone (outermost, blue, complete combustion, highest temperature). This is the standard structure of a candle flame.